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 $162.62   13.449%   $184.4908   $184.49   $184.50   $184.50  
  Purchase #2 $191.96   13.211%   $217.3198   $217.32   $217.30   $217.30  
  Purchase #3 $226.69   5.496%   $239.1489   $239.15   $239.15   $239.10  
  Purchase #4 $12.73   5.466%   $13.4258   $13.43   $13.45   $13.40  
  Purchase #5 $101.67   5.140%   $106.8958   $106.90   $106.90   $106.90  
  Purchase #6 $85.59   8.218%   $92.6238   $92.62   $92.60   $92.60  
  Purchase #7 $207.65   11.707%   $231.9596   $231.96   $231.95   $232.00  
  7 purchase totals = $988.91       $1,085.8645   $1,085.87   $1,085.85   $1,085.80