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 $61.92   9.147%   $67.5838   $67.58   $67.60   $67.60  
  Purchase #2 $33.88   6.519%   $36.0886   $36.09   $36.10   $36.10  
  Purchase #3 $180.82   13.656%   $205.5128   $205.51   $205.50   $205.50  
  Purchase #4 $54.64   7.189%   $58.5681   $58.57   $58.55   $58.60  
  Purchase #5 $212.52   8.188%   $229.9211   $229.92   $229.90   $229.90  
  Purchase #6 $52.27   8.410%   $56.6659   $56.67   $56.65   $56.70  
  Purchase #7 $228.55   6.811%   $244.1165   $244.12   $244.10   $244.10  
  7 purchase totals = $824.60       $898.4568   $898.46   $898.40   $898.50