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 $178.34   13.117%   $201.7329   $201.73   $201.75   $201.70  
  Purchase #2 $56.37   13.260%   $63.8447   $63.84   $63.85   $63.80  
  Purchase #3 $168.60   7.788%   $181.7306   $181.73   $181.75   $181.70  
  Purchase #4 $245.41   3.477%   $253.9429   $253.94   $253.95   $253.90  
  Purchase #5 $74.90   3.512%   $77.5305   $77.53   $77.55   $77.50  
  Purchase #6 $39.75   3.117%   $40.989   $40.99   $41.00   $41.00  
  Purchase #7 $120.58   5.435%   $127.1335   $127.13   $127.15   $127.10  
  7 purchase totals = $883.95       $946.9041   $946.89   $947.00   $946.70