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 $236.93   11.490%   $264.1533   $264.15   $264.15   $264.20  
  Purchase #2 $191.54   3.240%   $197.7459   $197.75   $197.75   $197.70  
  Purchase #3 $181.29   5.326%   $190.9455   $190.95   $190.95   $190.90  
  Purchase #4 $166.49   10.378%   $183.7683   $183.77   $183.75   $183.80  
  Purchase #5 $245.28   12.606%   $276.2   $276.20   $276.20   $276.20  
  Purchase #6 $98.91   5.157%   $104.0108   $104.01   $104.00   $104.00  
  Purchase #7 $201.60   6.164%   $214.0266   $214.03   $214.05   $214.00  
  7 purchase totals = $1,322.04       $1,430.8504   $1,430.86   $1,430.85   $1,430.80