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 $148.73   11.772%   $166.2385   $166.24   $166.25   $166.20  
  Purchase #2 $58.58   5.835%   $61.9981   $62.00   $62.00   $62.00  
  Purchase #3 $232.46   6.857%   $248.3998   $248.40   $248.40   $248.40  
  Purchase #4 $189.64   4.289%   $197.7737   $197.77   $197.75   $197.80  
  Purchase #5 $229.74   6.612%   $244.9304   $244.93   $244.95   $244.90  
  Purchase #6 $33.92   7.390%   $36.4267   $36.43   $36.45   $36.40  
  Purchase #7 $127.27   9.153%   $138.919   $138.92   $138.90   $138.90  
  7 purchase totals = $1,020.34       $1,094.6862   $1,094.69   $1,094.70   $1,094.60