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 $185.78   8.539%   $201.6438   $201.64   $201.65   $201.60  
  Purchase #2 $217.42   10.146%   $239.4794   $239.48   $239.50   $239.50  
  Purchase #3 $11.86   3.456%   $12.2699   $12.27   $12.25   $12.30  
  Purchase #4 $151.99   4.528%   $158.8721   $158.87   $158.85   $158.90  
  Purchase #5 $130.43   12.252%   $146.4103   $146.41   $146.40   $146.40  
  Purchase #6 $50.54   9.676%   $55.4303   $55.43   $55.45   $55.40  
  Purchase #7 $206.82   6.847%   $220.981   $220.98   $221.00   $221.00  
  7 purchase totals = $954.84       $1,035.0868   $1,035.08   $1,035.10   $1,035.10