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 $233.53   12.578%   $262.9034   $262.90   $262.90   $262.90  
  Purchase #2 $67.39   12.332%   $75.7005   $75.70   $75.70   $75.70  
  Purchase #3 $91.32   9.119%   $99.6475   $99.65   $99.65   $99.60  
  Purchase #4 $89.39   9.559%   $97.9348   $97.93   $97.95   $97.90  
  Purchase #5 $156.75   6.693%   $167.2413   $167.24   $167.25   $167.20  
  Purchase #6 $197.87   12.725%   $223.049   $223.05   $223.05   $223.00  
  Purchase #7 $40.61   5.389%   $42.7985   $42.80   $42.80   $42.80  
  7 purchase totals = $876.86       $969.2750   $969.27   $969.30   $969.10