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 $228.77   8.113%   $247.3301   $247.33   $247.35   $247.30  
  Purchase #2 $212.85   10.206%   $234.5735   $234.57   $234.55   $234.60  
  Purchase #3 $56.96   8.778%   $61.9599   $61.96   $61.95   $62.00  
  Purchase #4 $160.84   10.209%   $177.2602   $177.26   $177.25   $177.30  
  Purchase #5 $237.34   7.569%   $255.3043   $255.30   $255.30   $255.30  
  Purchase #6 $167.51   5.478%   $176.6862   $176.69   $176.70   $176.70  
  Purchase #7 $107.32   9.474%   $117.4875   $117.49   $117.50   $117.50  
  7 purchase totals = $1,171.59       $1,270.6017   $1,270.60   $1,270.60   $1,270.70