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 $45.98   10.121%   $50.6336   $50.63   $50.65   $50.60  
  Purchase #2 $175.39   6.719%   $187.1745   $187.17   $187.15   $187.20  
  Purchase #3 $123.98   8.721%   $134.7923   $134.79   $134.80   $134.80  
  Purchase #4 $208.64   3.194%   $215.304   $215.30   $215.30   $215.30  
  Purchase #5 $91.86   11.783%   $102.6839   $102.68   $102.70   $102.70  
  Purchase #6 $166.91   4.862%   $175.0252   $175.03   $175.05   $175.00  
  Purchase #7 $180.83   9.615%   $198.2168   $198.22   $198.20   $198.20  
  7 purchase totals = $993.59       $1,063.8303   $1,063.82   $1,063.85   $1,063.80