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 $44.82   11.217%   $49.8475   $49.85   $49.85   $49.80  
  Purchase #2 $187.57   6.283%   $199.355   $199.36   $199.35   $199.40  
  Purchase #3 $82.79   10.279%   $91.3   $91.30   $91.30   $91.30  
  Purchase #4 $149.43   5.671%   $157.9042   $157.90   $157.90   $157.90  
  Purchase #5 $96.39   10.230%   $106.2507   $106.25   $106.25   $106.30  
  Purchase #6 $9.75   8.509%   $10.5796   $10.58   $10.60   $10.60  
  Purchase #7 $34.36   10.650%   $38.0193   $38.02   $38.00   $38.00  
  7 purchase totals = $605.11       $653.2563   $653.26   $653.25   $653.30