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 $222.92   8.467%   $241.7946   $241.79   $241.80   $241.80  
  Purchase #2 $161.90   7.387%   $173.8596   $173.86   $173.85   $173.90  
  Purchase #3 $21.93   13.654%   $24.9243   $24.92   $24.90   $24.90  
  Purchase #4 $175.62   3.868%   $182.413   $182.41   $182.40   $182.40  
  Purchase #5 $151.70   3.434%   $156.9094   $156.91   $156.90   $156.90  
  Purchase #6 $231.97   13.502%   $263.2906   $263.29   $263.30   $263.30  
  Purchase #7 $154.29   13.372%   $174.9217   $174.92   $174.90   $174.90  
  7 purchase totals = $1,120.33       $1,218.1132   $1,218.10   $1,218.05   $1,218.10