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 $163.62   13.524%   $185.748   $185.75   $185.75   $185.70  
  Purchase #2 $150.74   12.740%   $169.9443   $169.94   $169.95   $169.90  
  Purchase #3 $73.54   10.459%   $81.2315   $81.23   $81.25   $81.20  
  Purchase #4 $27.29   9.217%   $29.8053   $29.81   $29.80   $29.80  
  Purchase #5 $82.98   5.329%   $87.402   $87.40   $87.40   $87.40  
  Purchase #6 $189.28   8.152%   $204.7101   $204.71   $204.70   $204.70  
  Purchase #7 $233.35   4.587%   $244.0538   $244.05   $244.05   $244.10  
  7 purchase totals = $920.80       $1,002.8950   $1,002.89   $1,002.90   $1,002.80