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 $197.92   13.697%   $225.0291   $225.03   $225.05   $225.00  
  Purchase #2 $166.91   5.240%   $175.6561   $175.66   $175.65   $175.70  
  Purchase #3 $213.44   9.261%   $233.2067   $233.21   $233.20   $233.20  
  Purchase #4 $103.27   3.173%   $106.5468   $106.55   $106.55   $106.50  
  Purchase #5 $57.44   4.592%   $60.0776   $60.08   $60.10   $60.10  
  Purchase #6 $43.32   8.128%   $46.841   $46.84   $46.85   $46.80  
  Purchase #7 $168.54   3.720%   $174.8097   $174.81   $174.80   $174.80  
  7 purchase totals = $950.84       $1,022.1670   $1,022.18   $1,022.20   $1,022.10