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 $77.67   13.379%   $88.0615   $88.06   $88.05   $88.10  
  Purchase #2 $111.57   4.114%   $116.16   $116.16   $116.15   $116.20  
  Purchase #3 $77.35   5.167%   $81.3467   $81.35   $81.35   $81.30  
  Purchase #4 $38.56   5.542%   $40.697   $40.70   $40.70   $40.70  
  Purchase #5 $86.77   11.507%   $96.7546   $96.75   $96.75   $96.80  
  Purchase #6 $34.43   5.411%   $36.293   $36.29   $36.30   $36.30  
  Purchase #7 $181.85   11.253%   $202.3136   $202.31   $202.30   $202.30  
  7 purchase totals = $608.20       $661.6264   $661.62   $661.60   $661.70