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 $49.96   10.565%   $55.2383   $55.24   $55.25   $55.20  
  Purchase #2 $174.84   11.329%   $194.6476   $194.65   $194.65   $194.60  
  Purchase #3 $152.38   9.485%   $166.8332   $166.83   $166.85   $166.80  
  Purchase #4 $100.32   13.552%   $113.9154   $113.92   $113.90   $113.90  
  Purchase #5 $218.96   11.486%   $244.1097   $244.11   $244.10   $244.10  
  Purchase #6 $50.91   4.448%   $53.1745   $53.17   $53.15   $53.20  
  Purchase #7 $180.61   12.558%   $203.291   $203.29   $203.30   $203.30  
  7 purchase totals = $927.98       $1,031.2097   $1,031.21   $1,031.20   $1,031.10