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 $65.46   5.441%   $69.0217   $69.02   $69.00   $69.00  
  Purchase #2 $237.60   11.470%   $264.8527   $264.85   $264.85   $264.90  
  Purchase #3 $199.26   6.471%   $212.1541   $212.15   $212.15   $212.20  
  Purchase #4 $136.41   3.619%   $141.3467   $141.35   $141.35   $141.30  
  Purchase #5 $45.53   4.163%   $47.4254   $47.43   $47.45   $47.40  
  Purchase #6 $107.92   13.804%   $122.8173   $122.82   $122.80   $122.80  
  Purchase #7 $95.42   4.342%   $99.5631   $99.56   $99.55   $99.60  
  7 purchase totals = $887.60       $957.1810   $957.18   $957.15   $957.20