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 $34.26   8.177%   $37.0614   $37.06   $37.05   $37.10  
  Purchase #2 $87.71   7.400%   $94.2005   $94.20   $94.20   $94.20  
  Purchase #3 $225.77   9.217%   $246.5792   $246.58   $246.60   $246.60  
  Purchase #4 $118.81   10.507%   $131.2934   $131.29   $131.30   $131.30  
  Purchase #5 $164.93   8.452%   $178.8699   $178.87   $178.85   $178.90  
  Purchase #6 $115.33   5.335%   $121.4829   $121.48   $121.50   $121.50  
  Purchase #7 $84.29   3.340%   $87.1053   $87.11   $87.10   $87.10  
  7 purchase totals = $831.10       $896.5926   $896.59   $896.60   $896.70