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 $219.69   8.423%   $238.1945   $238.19   $238.20   $238.20  
  Purchase #2 $206.86   9.733%   $226.9937   $226.99   $227.00   $227.00  
  Purchase #3 $163.73   9.726%   $179.6544   $179.65   $179.65   $179.70  
  Purchase #4 $58.62   5.683%   $61.9514   $61.95   $61.95   $62.00  
  Purchase #5 $52.38   9.455%   $57.3325   $57.33   $57.35   $57.30  
  Purchase #6 $52.85   3.721%   $54.8165   $54.82   $54.80   $54.80  
  Purchase #7 $173.62   6.250%   $184.4713   $184.47   $184.45   $184.50  
  7 purchase totals = $927.75       $1,003.4143   $1,003.40   $1,003.40   $1,003.50