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 $86.35   8.786%   $93.9367   $93.94   $93.95   $93.90  
  Purchase #2 $111.72   9.119%   $121.9077   $121.91   $121.90   $121.90  
  Purchase #3 $245.98   12.466%   $276.6439   $276.64   $276.65   $276.60  
  Purchase #4 $159.38   12.813%   $179.8014   $179.80   $179.80   $179.80  
  Purchase #5 $59.85   12.799%   $67.5102   $67.51   $67.50   $67.50  
  Purchase #6 $11.35   9.205%   $12.3948   $12.39   $12.40   $12.40  
  Purchase #7 $90.56   11.523%   $100.9952   $101.00   $101.00   $101.00  
  7 purchase totals = $765.19       $853.1899   $853.19   $853.20   $853.10