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 $159.26   4.463%   $166.3678   $166.37   $166.35   $166.40  
  Purchase #2 $76.68   8.395%   $83.1173   $83.12   $83.10   $83.10  
  Purchase #3 $181.45   7.753%   $195.5178   $195.52   $195.50   $195.50  
  Purchase #4 $33.67   4.645%   $35.234   $35.23   $35.25   $35.20  
  Purchase #5 $102.91   11.528%   $114.7735   $114.77   $114.75   $114.80  
  Purchase #6 $220.26   6.475%   $234.5218   $234.52   $234.50   $234.50  
  Purchase #7 $152.84   7.163%   $163.7879   $163.79   $163.80   $163.80  
  7 purchase totals = $927.07       $993.3201   $993.32   $993.25   $993.30