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 $228.26   8.704%   $248.1278   $248.13   $248.15   $248.10  
  Purchase #2 $83.93   13.567%   $95.3168   $95.32   $95.30   $95.30  
  Purchase #3 $168.48   10.570%   $186.2883   $186.29   $186.30   $186.30  
  Purchase #4 $144.75   4.123%   $150.718   $150.72   $150.70   $150.70  
  Purchase #5 $184.25   9.546%   $201.8385   $201.84   $201.85   $201.80  
  Purchase #6 $240.57   10.610%   $266.0945   $266.09   $266.10   $266.10  
  Purchase #7 $140.78   11.431%   $156.8726   $156.87   $156.85   $156.90  
  7 purchase totals = $1,191.02       $1,305.2565   $1,305.26   $1,305.25   $1,305.20