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 $86.47   11.446%   $96.3674   $96.37   $96.35   $96.40  
  Purchase #2 $89.84   8.502%   $97.4782   $97.48   $97.50   $97.50  
  Purchase #3 $246.52   6.440%   $262.3959   $262.40   $262.40   $262.40  
  Purchase #4 $124.36   11.628%   $138.8206   $138.82   $138.80   $138.80  
  Purchase #5 $125.67   12.593%   $141.4956   $141.50   $141.50   $141.50  
  Purchase #6 $140.39   5.332%   $147.8756   $147.88   $147.90   $147.90  
  Purchase #7 $64.76   10.532%   $71.5805   $71.58   $71.60   $71.60  
  7 purchase totals = $878.01       $956.0138   $956.03   $956.05   $956.10