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 $54.31   13.717%   $61.7597   $61.76   $61.75   $61.80  
  Purchase #2 $98.68   11.621%   $110.1476   $110.15   $110.15   $110.10  
  Purchase #3 $132.68   6.166%   $140.861   $140.86   $140.85   $140.90  
  Purchase #4 $241.41   11.240%   $268.5445   $268.54   $268.55   $268.50  
  Purchase #5 $48.63   5.529%   $51.3188   $51.32   $51.30   $51.30  
  Purchase #6 $124.29   6.736%   $132.6622   $132.66   $132.65   $132.70  
  Purchase #7 $199.62   11.760%   $223.0953   $223.10   $223.10   $223.10  
  7 purchase totals = $899.62       $988.3891   $988.39   $988.35   $988.40