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 $165.26   6.614%   $176.1903   $176.19   $176.20   $176.20  
  Purchase #2 $35.67   9.473%   $39.049   $39.05   $39.05   $39.00  
  Purchase #3 $218.27   10.178%   $240.4855   $240.49   $240.50   $240.50  
  Purchase #4 $66.71   12.853%   $75.2842   $75.28   $75.30   $75.30  
  Purchase #5 $24.27   9.814%   $26.6519   $26.65   $26.65   $26.70  
  Purchase #6 $55.37   5.640%   $58.4929   $58.49   $58.50   $58.50  
  Purchase #7 $176.70   4.819%   $185.2152   $185.22   $185.20   $185.20  
  7 purchase totals = $742.25       $801.3690   $801.37   $801.40   $801.40