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 $241.63   13.382%   $273.9649   $273.96   $273.95   $274.00  
  Purchase #2 $187.95   3.557%   $194.6354   $194.64   $194.65   $194.60  
  Purchase #3 $207.59   8.403%   $225.0338   $225.03   $225.05   $225.00  
  Purchase #4 $25.93   4.799%   $27.1744   $27.17   $27.15   $27.20  
  Purchase #5 $194.95   3.826%   $202.4088   $202.41   $202.40   $202.40  
  Purchase #6 $89.64   9.824%   $98.4462   $98.45   $98.45   $98.40  
  Purchase #7 $84.89   8.707%   $92.2814   $92.28   $92.30   $92.30  
  7 purchase totals = $1,032.58       $1,113.9449   $1,113.94   $1,113.95   $1,113.90