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 $35.30   9.737%   $38.7372   $38.74   $38.75   $38.70  
  Purchase #2 $232.62   12.874%   $262.5675   $262.57   $262.55   $262.60  
  Purchase #3 $221.77   10.356%   $244.7365   $244.74   $244.75   $244.70  
  Purchase #4 $189.90   8.128%   $205.3351   $205.34   $205.35   $205.30  
  Purchase #5 $136.85   8.670%   $148.7149   $148.71   $148.70   $148.70  
  Purchase #6 $16.59   5.837%   $17.5584   $17.56   $17.55   $17.60  
  Purchase #7 $40.99   10.661%   $45.3599   $45.36   $45.35   $45.40  
  7 purchase totals = $874.02       $963.0095   $963.02   $963.00   $963.00