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 $92.52   3.364%   $95.6324   $95.63   $95.65   $95.60  
  Purchase #2 $8.57   3.734%   $8.89   $8.89   $8.90   $8.90  
  Purchase #3 $70.61   13.484%   $80.1311   $80.13   $80.15   $80.10  
  Purchase #4 $114.35   8.606%   $124.191   $124.19   $124.20   $124.20  
  Purchase #5 $202.57   8.321%   $219.4258   $219.43   $219.45   $219.40  
  Purchase #6 $150.97   9.238%   $164.9166   $164.92   $164.90   $164.90  
  Purchase #7 $250.60   5.327%   $263.9495   $263.95   $263.95   $263.90  
  7 purchase totals = $890.19       $957.1364   $957.14   $957.20   $957.00