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 $82.49   12.413%   $92.7295   $92.73   $92.75   $92.70  
  Purchase #2 $71.95   3.698%   $74.6107   $74.61   $74.60   $74.60  
  Purchase #3 $169.69   8.672%   $184.4055   $184.41   $184.40   $184.40  
  Purchase #4 $204.56   10.223%   $225.4722   $225.47   $225.45   $225.50  
  Purchase #5 $10.77   13.322%   $12.2048   $12.20   $12.20   $12.20  
  Purchase #6 $168.35   11.295%   $187.3651   $187.37   $187.35   $187.40  
  Purchase #7 $249.80   5.695%   $264.0261   $264.03   $264.05   $264.00  
  7 purchase totals = $957.61       $1,040.8139   $1,040.82   $1,040.80   $1,040.80