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 $83.63   5.671%   $88.3727   $88.37   $88.35   $88.40  
  Purchase #2 $188.59   7.447%   $202.6343   $202.63   $202.65   $202.60  
  Purchase #3 $119.75   10.718%   $132.5848   $132.58   $132.60   $132.60  
  Purchase #4 $208.60   11.457%   $232.4993   $232.50   $232.50   $232.50  
  Purchase #5 $245.94   12.416%   $276.4759   $276.48   $276.50   $276.50  
  Purchase #6 $65.80   4.617%   $68.838   $68.84   $68.85   $68.80  
  Purchase #7 $127.81   10.439%   $141.1521   $141.15   $141.15   $141.20  
  7 purchase totals = $1,040.12       $1,142.5571   $1,142.55   $1,142.60   $1,142.60