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 $111.89   11.761%   $125.0494   $125.05   $125.05   $125.00  
  Purchase #2 $128.63   9.637%   $141.0261   $141.03   $141.05   $141.00  
  Purchase #3 $170.66   13.721%   $194.0763   $194.08   $194.10   $194.10  
  Purchase #4 $223.30   13.472%   $253.383   $253.38   $253.40   $253.40  
  Purchase #5 $229.76   9.813%   $252.3063   $252.31   $252.30   $252.30  
  Purchase #6 $108.86   9.355%   $119.0439   $119.04   $119.05   $119.00  
  Purchase #7 $165.76   3.673%   $171.8484   $171.85   $171.85   $171.80  
  7 purchase totals = $1,138.86       $1,256.7334   $1,256.74   $1,256.80   $1,256.60