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 $55.59   8.514%   $60.3229   $60.32   $60.30   $60.30  
  Purchase #2 $87.99   10.610%   $97.3257   $97.33   $97.35   $97.30  
  Purchase #3 $146.42   5.133%   $153.9357   $153.94   $153.95   $153.90  
  Purchase #4 $92.28   7.706%   $99.3911   $99.39   $99.40   $99.40  
  Purchase #5 $213.66   13.794%   $243.1323   $243.13   $243.15   $243.10  
  Purchase #6 $85.91   12.646%   $96.7742   $96.77   $96.75   $96.80  
  Purchase #7 $97.52   10.497%   $107.7567   $107.76   $107.75   $107.80  
  7 purchase totals = $779.37       $858.6386   $858.64   $858.65   $858.60