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 $71.65   5.484%   $75.5793   $75.58   $75.60   $75.60  
  Purchase #2 $191.94   4.767%   $201.0898   $201.09   $201.10   $201.10  
  Purchase #3 $112.49   3.808%   $116.7736   $116.77   $116.75   $116.80  
  Purchase #4 $148.79   7.441%   $159.8615   $159.86   $159.85   $159.90  
  Purchase #5 $87.49   4.551%   $91.4717   $91.47   $91.45   $91.50  
  Purchase #6 $59.68   3.589%   $61.8219   $61.82   $61.80   $61.80  
  Purchase #7 $132.92   6.132%   $141.0707   $141.07   $141.05   $141.10  
  7 purchase totals = $804.96       $847.6685   $847.66   $847.60   $847.80