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 $76.26   11.313%   $84.8873   $84.89   $84.90   $84.90  
  Purchase #2 $44.41   3.483%   $45.9568   $45.96   $45.95   $46.00  
  Purchase #3 $91.88   11.229%   $102.1972   $102.20   $102.20   $102.20  
  Purchase #4 $138.28   11.673%   $154.4214   $154.42   $154.40   $154.40  
  Purchase #5 $142.79   12.464%   $160.5873   $160.59   $160.60   $160.60  
  Purchase #6 $46.42   11.638%   $51.8224   $51.82   $51.80   $51.80  
  Purchase #7 $155.31   12.439%   $174.629   $174.63   $174.65   $174.60  
  7 purchase totals = $695.35       $774.5014   $774.51   $774.50   $774.50