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 $92.32   5.756%   $97.6339   $97.63   $97.65   $97.60  
  Purchase #2 $181.68   12.465%   $204.3264   $204.33   $204.35   $204.30  
  Purchase #3 $237.81   5.193%   $250.1595   $250.16   $250.15   $250.20  
  Purchase #4 $40.27   6.815%   $43.0144   $43.01   $43.00   $43.00  
  Purchase #5 $245.85   13.563%   $279.1946   $279.19   $279.20   $279.20  
  Purchase #6 $160.66   10.569%   $177.6402   $177.64   $177.65   $177.60  
  Purchase #7 $177.84   10.661%   $196.7995   $196.80   $196.80   $196.80  
  7 purchase totals = $1,136.43       $1,248.7685   $1,248.76   $1,248.80   $1,248.70