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 $164.66   11.644%   $183.833   $183.83   $183.85   $183.80  
  Purchase #2 $165.45   13.471%   $187.7378   $187.74   $187.75   $187.70  
  Purchase #3 $233.74   5.846%   $247.4044   $247.40   $247.40   $247.40  
  Purchase #4 $169.66   4.255%   $176.879   $176.88   $176.90   $176.90  
  Purchase #5 $233.35   4.721%   $244.3665   $244.37   $244.35   $244.40  
  Purchase #6 $235.25   12.202%   $263.9552   $263.96   $263.95   $264.00  
  Purchase #7 $8.71   12.633%   $9.8103   $9.81   $9.80   $9.80  
  7 purchase totals = $1,210.82       $1,313.9862   $1,313.99   $1,314.00   $1,314.00