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 $76.36   12.131%   $85.6232   $85.62   $85.60   $85.60  
  Purchase #2 $113.83   5.394%   $119.97   $119.97   $119.95   $120.00  
  Purchase #3 $188.68   4.795%   $197.7272   $197.73   $197.75   $197.70  
  Purchase #4 $233.51   5.156%   $245.5498   $245.55   $245.55   $245.50  
  Purchase #5 $230.36   10.230%   $253.9258   $253.93   $253.95   $253.90  
  Purchase #6 $202.75   12.113%   $227.3091   $227.31   $227.30   $227.30  
  Purchase #7 $172.36   5.501%   $181.8415   $181.84   $181.85   $181.80  
  7 purchase totals = $1,217.85       $1,311.9466   $1,311.95   $1,311.95   $1,311.80