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 $179.47   8.517%   $194.7555   $194.76   $194.75   $194.80  
  Purchase #2 $242.52   8.582%   $263.3331   $263.33   $263.35   $263.30  
  Purchase #3 $62.54   7.494%   $67.2267   $67.23   $67.25   $67.20  
  Purchase #4 $64.47   3.851%   $66.9527   $66.95   $66.95   $67.00  
  Purchase #5 $165.39   9.223%   $180.6439   $180.64   $180.65   $180.60  
  Purchase #6 $8.95   7.178%   $9.5924   $9.59   $9.60   $9.60  
  Purchase #7 $156.55   9.739%   $171.7964   $171.80   $171.80   $171.80  
  7 purchase totals = $879.89       $954.3007   $954.30   $954.35   $954.30