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 $71.99   5.554%   $75.9883   $75.99   $76.00   $76.00  
  Purchase #2 $145.34   3.447%   $150.3499   $150.35   $150.35   $150.30  
  Purchase #3 $159.53   7.152%   $170.9396   $170.94   $170.95   $170.90  
  Purchase #4 $230.88   5.474%   $243.5184   $243.52   $243.50   $243.50  
  Purchase #5 $177.70   5.130%   $186.816   $186.82   $186.80   $186.80  
  Purchase #6 $219.87   7.708%   $236.8176   $236.82   $236.80   $236.80  
  Purchase #7 $233.37   7.667%   $251.2625   $251.26   $251.25   $251.30  
  7 purchase totals = $1,238.68       $1,315.6923   $1,315.70   $1,315.65   $1,315.60