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 $114.94   10.640%   $127.1696   $127.17   $127.15   $127.20  
  Purchase #2 $72.78   12.579%   $81.935   $81.94   $81.95   $81.90  
  Purchase #3 $205.59   10.284%   $226.7329   $226.73   $226.75   $226.70  
  Purchase #4 $76.69   8.744%   $83.3958   $83.40   $83.40   $83.40  
  Purchase #5 $59.37   3.148%   $61.239   $61.24   $61.25   $61.20  
  Purchase #6 $184.67   6.741%   $197.1186   $197.12   $197.10   $197.10  
  Purchase #7 $223.66   5.594%   $236.1715   $236.17   $236.15   $236.20  
  7 purchase totals = $937.70       $1,013.7624   $1,013.77   $1,013.75   $1,013.70