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 $206.53   9.437%   $226.0202   $226.02   $226.00   $226.00  
  Purchase #2 $150.36   6.276%   $159.7966   $159.80   $159.80   $159.80  
  Purchase #3 $181.82   7.740%   $195.8929   $195.89   $195.90   $195.90  
  Purchase #4 $161.31   13.181%   $182.5723   $182.57   $182.55   $182.60  
  Purchase #5 $120.99   3.534%   $125.2658   $125.27   $125.25   $125.30  
  Purchase #6 $111.47   11.404%   $124.182   $124.18   $124.20   $124.20  
  Purchase #7 $203.69   9.484%   $223.008   $223.01   $223.00   $223.00  
  7 purchase totals = $1,136.17       $1,236.7378   $1,236.74   $1,236.70   $1,236.80