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 $128.76   6.202%   $136.7457   $136.75   $136.75   $136.70  
  Purchase #2 $32.27   4.625%   $33.7625   $33.76   $33.75   $33.80  
  Purchase #3 $212.39   13.701%   $241.4896   $241.49   $241.50   $241.50  
  Purchase #4 $228.61   9.142%   $249.5095   $249.51   $249.50   $249.50  
  Purchase #5 $69.80   10.258%   $76.9601   $76.96   $76.95   $77.00  
  Purchase #6 $217.48   12.154%   $243.9125   $243.91   $243.90   $243.90  
  Purchase #7 $199.42   11.160%   $221.6753   $221.68   $221.70   $221.70  
  7 purchase totals = $1,088.73       $1,204.0552   $1,204.06   $1,204.05   $1,204.10