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 $228.69   8.534%   $248.2064   $248.21   $248.20   $248.20  
  Purchase #2 $215.80   9.392%   $236.0679   $236.07   $236.05   $236.10  
  Purchase #3 $93.33   9.851%   $102.5239   $102.52   $102.50   $102.50  
  Purchase #4 $107.51   3.243%   $110.9965   $111.00   $111.00   $111.00  
  Purchase #5 $237.79   6.535%   $253.3296   $253.33   $253.35   $253.30  
  Purchase #6 $46.78   8.589%   $50.7979   $50.80   $50.80   $50.80  
  Purchase #7 $246.78   13.821%   $280.8875   $280.89   $280.90   $280.90  
  7 purchase totals = $1,176.68       $1,282.8097   $1,282.82   $1,282.80   $1,282.80