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 $116.99   8.698%   $127.1658   $127.17   $127.15   $127.20  
  Purchase #2 $86.55   5.330%   $91.1631   $91.16   $91.15   $91.20  
  Purchase #3 $27.39   3.666%   $28.3941   $28.39   $28.40   $28.40  
  Purchase #4 $246.35   11.538%   $274.7739   $274.77   $274.75   $274.80  
  Purchase #5 $180.31   7.151%   $193.204   $193.20   $193.20   $193.20  
  Purchase #6 $236.82   11.352%   $263.7038   $263.70   $263.70   $263.70  
  Purchase #7 $39.67   10.811%   $43.9587   $43.96   $43.95   $44.00  
  7 purchase totals = $934.08       $1,022.3634   $1,022.35   $1,022.30   $1,022.50