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 $155.65   12.454%   $175.0347   $175.03   $175.05   $175.00  
  Purchase #2 $43.43   13.502%   $49.2939   $49.29   $49.30   $49.30  
  Purchase #3 $65.88   13.775%   $74.955   $74.96   $74.95   $75.00  
  Purchase #4 $57.31   8.131%   $61.9699   $61.97   $61.95   $62.00  
  Purchase #5 $182.35   9.520%   $199.7097   $199.71   $199.70   $199.70  
  Purchase #6 $78.58   11.866%   $87.9043   $87.90   $87.90   $87.90  
  Purchase #7 $187.37   12.144%   $210.1242   $210.12   $210.10   $210.10  
  7 purchase totals = $770.57       $858.9917   $858.98   $858.95   $859.00