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 $34.86   8.350%   $37.7708   $37.77   $37.75   $37.80  
  Purchase #2 $177.99   4.797%   $186.5282   $186.53   $186.55   $186.50  
  Purchase #3 $29.38   8.556%   $31.8938   $31.89   $31.90   $31.90  
  Purchase #4 $228.87   7.756%   $246.6212   $246.62   $246.60   $246.60  
  Purchase #5 $54.54   13.839%   $62.0878   $62.09   $62.10   $62.10  
  Purchase #6 $241.82   8.253%   $261.7774   $261.78   $261.80   $261.80  
  Purchase #7 $240.57   7.286%   $258.0979   $258.10   $258.10   $258.10  
  7 purchase totals = $1,008.03       $1,084.7771   $1,084.78   $1,084.80   $1,084.80