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 $206.96   13.811%   $235.5432   $235.54   $235.55   $235.50  
  Purchase #2 $34.43   12.115%   $38.6012   $38.60   $38.60   $38.60  
  Purchase #3 $129.54   5.355%   $136.4769   $136.48   $136.50   $136.50  
  Purchase #4 $138.44   13.723%   $157.4381   $157.44   $157.45   $157.40  
  Purchase #5 $222.47   5.714%   $235.1819   $235.18   $235.20   $235.20  
  Purchase #6 $210.83   7.790%   $227.2537   $227.25   $227.25   $227.30  
  Purchase #7 $150.79   8.467%   $163.5574   $163.56   $163.55   $163.60  
  7 purchase totals = $1,093.46       $1,194.0524   $1,194.05   $1,194.10   $1,194.10