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 $211.78   11.451%   $236.0309   $236.03   $236.05   $236.00  
  Purchase #2 $71.74   10.535%   $79.2978   $79.30   $79.30   $79.30  
  Purchase #3 $39.57   12.750%   $44.6152   $44.62   $44.60   $44.60  
  Purchase #4 $51.70   12.765%   $58.2995   $58.30   $58.30   $58.30  
  Purchase #5 $119.58   5.529%   $126.1916   $126.19   $126.20   $126.20  
  Purchase #6 $141.28   13.505%   $160.3599   $160.36   $160.35   $160.40  
  Purchase #7 $74.87   11.709%   $83.6365   $83.64   $83.65   $83.60  
  7 purchase totals = $710.52       $788.4314   $788.44   $788.45   $788.40