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 $75.53   5.264%   $79.5059   $79.51   $79.50   $79.50  
  Purchase #2 $219.59   4.439%   $229.3376   $229.34   $229.35   $229.30  
  Purchase #3 $68.80   10.103%   $75.7509   $75.75   $75.75   $75.80  
  Purchase #4 $175.29   5.190%   $184.3876   $184.39   $184.40   $184.40  
  Purchase #5 $235.90   11.467%   $262.9507   $262.95   $262.95   $263.00  
  Purchase #6 $78.86   5.826%   $83.4544   $83.45   $83.45   $83.50  
  Purchase #7 $41.27   8.729%   $44.8725   $44.87   $44.85   $44.90  
  7 purchase totals = $895.24       $960.2596   $960.26   $960.25   $960.40