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 $106.74   6.143%   $113.297   $113.30   $113.30   $113.30  
  Purchase #2 $216.72   11.542%   $241.7338   $241.73   $241.75   $241.70  
  Purchase #3 $153.79   4.183%   $160.223   $160.22   $160.20   $160.20  
  Purchase #4 $132.26   13.326%   $149.885   $149.89   $149.90   $149.90  
  Purchase #5 $157.69   5.612%   $166.5396   $166.54   $166.55   $166.50  
  Purchase #6 $45.42   9.105%   $49.5555   $49.56   $49.55   $49.60  
  Purchase #7 $129.32   13.178%   $146.3618   $146.36   $146.35   $146.40  
  7 purchase totals = $941.94       $1,027.5957   $1,027.60   $1,027.60   $1,027.60