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 $79.85   8.870%   $86.9327   $86.93   $86.95   $86.90  
  Purchase #2 $30.71   9.224%   $33.5427   $33.54   $33.55   $33.50  
  Purchase #3 $225.73   12.797%   $254.6167   $254.62   $254.60   $254.60  
  Purchase #4 $184.83   8.153%   $199.8992   $199.90   $199.90   $199.90  
  Purchase #5 $67.68   3.374%   $69.9635   $69.96   $69.95   $70.00  
  Purchase #6 $167.35   4.443%   $174.7854   $174.79   $174.80   $174.80  
  Purchase #7 $201.97   6.200%   $214.4921   $214.49   $214.50   $214.50  
  7 purchase totals = $958.12       $1,034.2323   $1,034.23   $1,034.25   $1,034.20