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 $218.64   12.183%   $245.2769   $245.28   $245.30   $245.30  
  Purchase #2 $189.78   9.234%   $207.3043   $207.30   $207.30   $207.30  
  Purchase #3 $89.52   8.597%   $97.216   $97.22   $97.20   $97.20  
  Purchase #4 $14.78   11.381%   $16.4621   $16.46   $16.45   $16.50  
  Purchase #5 $100.25   13.312%   $113.5953   $113.60   $113.60   $113.60  
  Purchase #6 $245.32   5.116%   $257.8706   $257.87   $257.85   $257.90  
  Purchase #7 $137.52   13.785%   $156.4771   $156.48   $156.50   $156.50  
  7 purchase totals = $995.81       $1,094.2023   $1,094.21   $1,094.20   $1,094.30