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 $186.92   3.238%   $192.9725   $192.97   $192.95   $193.00  
  Purchase #2 $61.86   11.403%   $68.9139   $68.91   $68.90   $68.90  
  Purchase #3 $25.89   9.649%   $28.3881   $28.39   $28.40   $28.40  
  Purchase #4 $108.52   7.847%   $117.0356   $117.04   $117.05   $117.00  
  Purchase #5 $164.79   6.329%   $175.2196   $175.22   $175.20   $175.20  
  Purchase #6 $96.56   5.794%   $102.1547   $102.15   $102.15   $102.20  
  Purchase #7 $114.50   8.534%   $124.2714   $124.27   $124.25   $124.30  
  7 purchase totals = $759.04       $808.9558   $808.95   $808.90   $809.00