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 $98.38   3.747%   $102.0663   $102.07   $102.05   $102.10  
  Purchase #2 $6.70   12.367%   $7.5286   $7.53   $7.55   $7.50  
  Purchase #3 $27.60   11.637%   $30.8118   $30.81   $30.80   $30.80  
  Purchase #4 $166.52   10.696%   $184.331   $184.33   $184.35   $184.30  
  Purchase #5 $235.25   13.515%   $267.044   $267.04   $267.05   $267.00  
  Purchase #6 $105.51   12.781%   $118.9952   $119.00   $119.00   $119.00  
  Purchase #7 $19.52   8.188%   $21.1183   $21.12   $21.10   $21.10  
  7 purchase totals = $659.48       $731.8952   $731.90   $731.90   $731.80