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 $127.96   3.128%   $131.9626   $131.96   $131.95   $132.00  
  Purchase #2 $176.51   8.570%   $191.6369   $191.64   $191.65   $191.60  
  Purchase #3 $59.92   7.300%   $64.2942   $64.29   $64.30   $64.30  
  Purchase #4 $235.69   3.511%   $243.9651   $243.97   $243.95   $244.00  
  Purchase #5 $211.27   10.568%   $233.597   $233.60   $233.60   $233.60  
  Purchase #6 $20.45   5.860%   $21.6484   $21.65   $21.65   $21.60  
  Purchase #7 $10.31   10.585%   $11.4013   $11.40   $11.40   $11.40  
  7 purchase totals = $842.11       $898.5055   $898.51   $898.50   $898.50