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 $95.25   3.586%   $98.6657   $98.67   $98.65   $98.70  
  Purchase #2 $98.93   11.436%   $110.2436   $110.24   $110.25   $110.20  
  Purchase #3 $245.31   13.229%   $277.7621   $277.76   $277.75   $277.80  
  Purchase #4 $200.64   8.837%   $218.3706   $218.37   $218.35   $218.40  
  Purchase #5 $22.53   11.159%   $25.0441   $25.04   $25.05   $25.00  
  Purchase #6 $170.89   6.480%   $181.9637   $181.96   $181.95   $182.00  
  Purchase #7 $21.51   12.303%   $24.1564   $24.16   $24.15   $24.20  
  7 purchase totals = $855.06       $936.2062   $936.20   $936.15   $936.30