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 $25.37   6.538%   $27.0287   $27.03   $27.05   $27.00  
  Purchase #2 $219.27   10.346%   $241.9557   $241.96   $241.95   $242.00  
  Purchase #3 $92.72   4.753%   $97.127   $97.13   $97.15   $97.10  
  Purchase #4 $37.95   4.258%   $39.5659   $39.57   $39.55   $39.60  
  Purchase #5 $201.87   5.649%   $213.2736   $213.27   $213.25   $213.30  
  Purchase #6 $33.86   13.306%   $38.3654   $38.37   $38.35   $38.40  
  Purchase #7 $129.95   5.235%   $136.7529   $136.75   $136.75   $136.80  
  7 purchase totals = $740.99       $794.0692   $794.08   $794.05   $794.20