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 $41.29   4.319%   $43.0733   $43.07   $43.05   $43.10  
  Purchase #2 $173.75   5.133%   $182.6686   $182.67   $182.65   $182.70  
  Purchase #3 $194.76   3.480%   $201.5376   $201.54   $201.55   $201.50  
  Purchase #4 $32.63   9.395%   $35.6956   $35.70   $35.70   $35.70  
  Purchase #5 $245.37   9.180%   $267.895   $267.90   $267.90   $267.90  
  Purchase #6 $207.63   9.803%   $227.984   $227.98   $228.00   $228.00  
  Purchase #7 $107.50   13.693%   $122.22   $122.22   $122.20   $122.20  
  7 purchase totals = $1,002.93       $1,081.0741   $1,081.08   $1,081.05   $1,081.10