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 $65.66   4.228%   $68.4361   $68.44   $68.45   $68.40  
  Purchase #2 $95.81   3.251%   $98.9248   $98.92   $98.90   $98.90  
  Purchase #3 $196.43   7.745%   $211.6435   $211.64   $211.65   $211.60  
  Purchase #4 $190.53   7.467%   $204.7569   $204.76   $204.75   $204.80  
  Purchase #5 $239.34   8.761%   $260.3086   $260.31   $260.30   $260.30  
  Purchase #6 $225.58   13.470%   $255.9656   $255.97   $255.95   $256.00  
  Purchase #7 $132.71   13.451%   $150.5608   $150.56   $150.55   $150.60  
  7 purchase totals = $1,146.06       $1,250.5963   $1,250.60   $1,250.55   $1,250.60