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 $230.34   5.532%   $243.0824   $243.08   $243.10   $243.10  
  Purchase #2 $108.64   4.242%   $113.2485   $113.25   $113.25   $113.20  
  Purchase #3 $86.29   13.496%   $97.9357   $97.94   $97.95   $97.90  
  Purchase #4 $203.68   10.116%   $224.2843   $224.28   $224.30   $224.30  
  Purchase #5 $106.66   12.313%   $119.793   $119.79   $119.80   $119.80  
  Purchase #6 $161.69   10.159%   $178.1161   $178.12   $178.10   $178.10  
  Purchase #7 $158.74   10.495%   $175.3998   $175.40   $175.40   $175.40  
  7 purchase totals = $1,056.04       $1,151.8598   $1,151.86   $1,151.90   $1,151.80