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 $195.73   11.711%   $218.6519   $218.65   $218.65   $218.70  
  Purchase #2 $22.41   11.224%   $24.9253   $24.93   $24.95   $24.90  
  Purchase #3 $104.33   12.434%   $117.3024   $117.30   $117.30   $117.30  
  Purchase #4 $92.56   13.200%   $104.7779   $104.78   $104.80   $104.80  
  Purchase #5 $165.96   4.867%   $174.0373   $174.04   $174.05   $174.00  
  Purchase #6 $194.35   11.481%   $216.6633   $216.66   $216.65   $216.70  
  Purchase #7 $119.38   7.637%   $128.4971   $128.50   $128.50   $128.50  
  7 purchase totals = $894.72       $984.8552   $984.86   $984.90   $984.90