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 $212.58   6.206%   $225.7727   $225.77   $225.75   $225.80  
  Purchase #2 $200.39   3.465%   $207.3335   $207.33   $207.35   $207.30  
  Purchase #3 $62.34   13.848%   $70.9728   $70.97   $70.95   $71.00  
  Purchase #4 $7.52   6.731%   $8.0262   $8.03   $8.05   $8.00  
  Purchase #5 $62.46   3.365%   $64.5618   $64.56   $64.55   $64.60  
  Purchase #6 $54.75   12.502%   $61.5948   $61.59   $61.60   $61.60  
  Purchase #7 $7.70   10.821%   $8.5332   $8.53   $8.55   $8.50  
  7 purchase totals = $607.74       $646.7950   $646.78   $646.80   $646.80