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 $218.44   6.782%   $233.2546   $233.25   $233.25   $233.30  
  Purchase #2 $102.84   7.120%   $110.1622   $110.16   $110.15   $110.20  
  Purchase #3 $125.78   13.667%   $142.9704   $142.97   $142.95   $143.00  
  Purchase #4 $83.98   11.230%   $93.411   $93.41   $93.40   $93.40  
  Purchase #5 $215.52   9.227%   $235.406   $235.41   $235.40   $235.40  
  Purchase #6 $218.60   12.357%   $245.6124   $245.61   $245.60   $245.60  
  Purchase #7 $93.31   11.651%   $104.1815   $104.18   $104.20   $104.20  
  7 purchase totals = $1,058.47       $1,164.9981   $1,164.99   $1,164.95   $1,165.10