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 $243.53   6.599%   $259.6005   $259.60   $259.60   $259.60  
  Purchase #2 $67.97   8.524%   $73.7638   $73.76   $73.75   $73.80  
  Purchase #3 $101.84   11.439%   $113.4895   $113.49   $113.50   $113.50  
  Purchase #4 $225.39   12.328%   $253.1761   $253.18   $253.20   $253.20  
  Purchase #5 $201.87   8.645%   $219.3217   $219.32   $219.30   $219.30  
  Purchase #6 $103.26   4.348%   $107.7497   $107.75   $107.75   $107.70  
  Purchase #7 $54.86   10.160%   $60.4338   $60.43   $60.45   $60.40  
  7 purchase totals = $998.72       $1,087.5351   $1,087.53   $1,087.55   $1,087.50