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 $84.35   12.151%   $94.5994   $94.60   $94.60   $94.60  
  Purchase #2 $232.63   6.294%   $247.2717   $247.27   $247.25   $247.30  
  Purchase #3 $94.36   3.491%   $97.6541   $97.65   $97.65   $97.70  
  Purchase #4 $177.87   6.439%   $189.323   $189.32   $189.30   $189.30  
  Purchase #5 $61.48   5.738%   $65.0077   $65.01   $65.00   $65.00  
  Purchase #6 $128.93   3.458%   $133.3884   $133.39   $133.40   $133.40  
  Purchase #7 $198.42   13.682%   $225.5678   $225.57   $225.55   $225.60  
  7 purchase totals = $978.04       $1,052.8121   $1,052.81   $1,052.75   $1,052.90