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 $59.33   3.397%   $61.3454   $61.35   $61.35   $61.30  
  Purchase #2 $126.77   5.667%   $133.9541   $133.95   $133.95   $134.00  
  Purchase #3 $68.97   5.757%   $72.9406   $72.94   $72.95   $72.90  
  Purchase #4 $157.65   9.585%   $172.7608   $172.76   $172.75   $172.80  
  Purchase #5 $202.74   9.674%   $222.3531   $222.35   $222.35   $222.40  
  Purchase #6 $174.58   7.301%   $187.3261   $187.33   $187.35   $187.30  
  Purchase #7 $83.53   5.410%   $88.049   $88.05   $88.05   $88.00  
  7 purchase totals = $873.57       $938.7291   $938.73   $938.75   $938.70