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 $59.59   12.770%   $67.1996   $67.20   $67.20   $67.20  
  Purchase #2 $116.92   11.368%   $130.2115   $130.21   $130.20   $130.20  
  Purchase #3 $161.56   12.808%   $182.2526   $182.25   $182.25   $182.30  
  Purchase #4 $169.59   11.384%   $188.8961   $188.90   $188.90   $188.90  
  Purchase #5 $181.77   4.173%   $189.3553   $189.36   $189.35   $189.40  
  Purchase #6 $173.96   6.485%   $185.2413   $185.24   $185.25   $185.20  
  Purchase #7 $19.57   13.689%   $22.2489   $22.25   $22.25   $22.20  
  7 purchase totals = $882.96       $965.4053   $965.41   $965.40   $965.40