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 $45.88   8.221%   $49.6518   $49.65   $49.65   $49.70  
  Purchase #2 $55.57   6.536%   $59.2021   $59.20   $59.20   $59.20  
  Purchase #3 $72.55   13.444%   $82.3036   $82.30   $82.30   $82.30  
  Purchase #4 $187.37   3.511%   $193.9486   $193.95   $193.95   $193.90  
  Purchase #5 $123.87   8.805%   $134.7768   $134.78   $134.80   $134.80  
  Purchase #6 $44.60   4.420%   $46.5713   $46.57   $46.55   $46.60  
  Purchase #7 $169.69   12.411%   $190.7502   $190.75   $190.75   $190.80  
  7 purchase totals = $699.53       $757.2044   $757.20   $757.20   $757.30