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 $41.54   7.325%   $44.5828   $44.58   $44.60   $44.60  
  Purchase #2 $132.29   12.300%   $148.5617   $148.56   $148.55   $148.60  
  Purchase #3 $126.85   6.532%   $135.1358   $135.14   $135.15   $135.10  
  Purchase #4 $61.74   7.368%   $66.289   $66.29   $66.30   $66.30  
  Purchase #5 $65.65   5.122%   $69.0126   $69.01   $69.00   $69.00  
  Purchase #6 $168.66   10.581%   $186.5059   $186.51   $186.50   $186.50  
  Purchase #7 $61.36   3.307%   $63.3892   $63.39   $63.40   $63.40  
  7 purchase totals = $658.09       $713.4770   $713.48   $713.50   $713.50