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 $22.59   8.501%   $24.5104   $24.51   $24.50   $24.50  
  Purchase #2 $138.34   13.343%   $156.7987   $156.80   $156.80   $156.80  
  Purchase #3 $69.81   11.480%   $77.8242   $77.82   $77.80   $77.80  
  Purchase #4 $120.83   4.790%   $126.6178   $126.62   $126.60   $126.60  
  Purchase #5 $53.48   13.272%   $60.5779   $60.58   $60.60   $60.60  
  Purchase #6 $65.39   4.616%   $68.4084   $68.41   $68.40   $68.40  
  Purchase #7 $233.52   3.798%   $242.3891   $242.39   $242.40   $242.40  
  7 purchase totals = $703.96       $757.1265   $757.13   $757.10   $757.10