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 $53.99   12.340%   $60.6524   $60.65   $60.65   $60.70  
  Purchase #2 $227.95   8.147%   $246.5211   $246.52   $246.50   $246.50  
  Purchase #3 $210.26   6.570%   $224.0741   $224.07   $224.05   $224.10  
  Purchase #4 $57.78   6.867%   $61.7478   $61.75   $61.75   $61.70  
  Purchase #5 $216.56   4.822%   $227.0025   $227.00   $227.00   $227.00  
  Purchase #6 $194.69   5.154%   $204.7243   $204.72   $204.70   $204.70  
  Purchase #7 $180.86   3.321%   $186.8664   $186.87   $186.85   $186.90  
  7 purchase totals = $1,142.09       $1,211.5886   $1,211.58   $1,211.50   $1,211.60