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 $61.59   8.663%   $66.9255   $66.93   $66.95   $66.90  
  Purchase #2 $221.62   8.676%   $240.8478   $240.85   $240.85   $240.80  
  Purchase #3 $15.52   10.203%   $17.1035   $17.10   $17.10   $17.10  
  Purchase #4 $228.90   13.830%   $260.5569   $260.56   $260.55   $260.60  
  Purchase #5 $209.55   8.586%   $227.542   $227.54   $227.55   $227.50  
  Purchase #6 $192.49   13.152%   $217.8063   $217.81   $217.80   $217.80  
  Purchase #7 $96.60   3.721%   $100.1945   $100.19   $100.20   $100.20  
  7 purchase totals = $1,026.27       $1,130.9765   $1,130.98   $1,131.00   $1,130.90