Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $203.61   10.103%   $224.1807   $224.18   $224.20   $224.20  
  Purchase #2 $122.37   6.251%   $130.0193   $130.02   $130.00   $130.00  
  Purchase #3 $135.90   9.795%   $149.2114   $149.21   $149.20   $149.20  
  Purchase #4 $207.64   3.695%   $215.3123   $215.31   $215.30   $215.30  
  Purchase #5 $196.67   7.796%   $212.0024   $212.00   $212.00   $212.00  
  Purchase #6 $132.27   11.629%   $147.6517   $147.65   $147.65   $147.70  
  Purchase #7 $240.77   13.271%   $272.7226   $272.72   $272.70   $272.70  
  7 purchase totals = $1,239.23       $1,351.1004   $1,351.09   $1,351.05   $1,351.10