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 $66.80   3.668%   $69.2502   $69.25   $69.25   $69.30  
  Purchase #2 $182.61   5.391%   $192.4545   $192.45   $192.45   $192.50  
  Purchase #3 $119.50   8.762%   $129.9706   $129.97   $129.95   $130.00  
  Purchase #4 $238.46   5.197%   $250.8528   $250.85   $250.85   $250.90  
  Purchase #5 $76.68   10.634%   $84.8342   $84.83   $84.85   $84.80  
  Purchase #6 $230.70   10.283%   $254.4229   $254.42   $254.40   $254.40  
  Purchase #7 $39.27   10.810%   $43.5151   $43.52   $43.50   $43.50  
  7 purchase totals = $954.02       $1,025.3003   $1,025.29   $1,025.25   $1,025.40