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 $219.70   11.378%   $244.6975   $244.70   $244.70   $244.70  
  Purchase #2 $134.94   4.537%   $141.0622   $141.06   $141.05   $141.10  
  Purchase #3 $111.41   8.381%   $120.7473   $120.75   $120.75   $120.70  
  Purchase #4 $7.90   3.390%   $8.1678   $8.17   $8.15   $8.20  
  Purchase #5 $50.82   7.435%   $54.5985   $54.60   $54.60   $54.60  
  Purchase #6 $182.84   9.342%   $199.9209   $199.92   $199.90   $199.90  
  Purchase #7 $171.46   7.397%   $184.1429   $184.14   $184.15   $184.10  
  7 purchase totals = $879.07       $953.3371   $953.34   $953.30   $953.30