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 $84.37   9.856%   $92.6855   $92.69   $92.70   $92.70  
  Purchase #2 $112.38   8.381%   $121.7986   $121.80   $121.80   $121.80  
  Purchase #3 $244.71   11.412%   $272.6363   $272.64   $272.65   $272.60  
  Purchase #4 $82.93   9.867%   $91.1127   $91.11   $91.10   $91.10  
  Purchase #5 $144.69   5.645%   $152.8578   $152.86   $152.85   $152.90  
  Purchase #6 $23.61   7.679%   $25.423   $25.42   $25.40   $25.40  
  Purchase #7 $174.76   5.337%   $184.0869   $184.09   $184.10   $184.10  
  7 purchase totals = $867.45       $940.6008   $940.61   $940.60   $940.60