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 $57.62   5.142%   $60.5828   $60.58   $60.60   $60.60  
  Purchase #2 $237.34   11.541%   $264.7314   $264.73   $264.75   $264.70  
  Purchase #3 $193.49   7.542%   $208.083   $208.08   $208.10   $208.10  
  Purchase #4 $141.33   8.740%   $153.6822   $153.68   $153.70   $153.70  
  Purchase #5 $81.66   7.281%   $87.6057   $87.61   $87.60   $87.60  
  Purchase #6 $71.39   3.260%   $73.7173   $73.72   $73.70   $73.70  
  Purchase #7 $27.45   4.691%   $28.7377   $28.74   $28.75   $28.70  
  7 purchase totals = $810.28       $877.1401   $877.14   $877.20   $877.10