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 $54.88   11.601%   $61.2466   $61.25   $61.25   $61.20  
  Purchase #2 $161.71   5.285%   $170.2564   $170.26   $170.25   $170.30  
  Purchase #3 $85.98   9.254%   $93.9366   $93.94   $93.95   $93.90  
  Purchase #4 $219.76   8.603%   $238.666   $238.67   $238.65   $238.70  
  Purchase #5 $99.67   7.298%   $106.9439   $106.94   $106.95   $106.90  
  Purchase #6 $57.52   7.214%   $61.6695   $61.67   $61.65   $61.70  
  Purchase #7 $231.96   12.814%   $261.6834   $261.68   $261.70   $261.70  
  7 purchase totals = $911.48       $994.4024   $994.41   $994.40   $994.40