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 $209.47   3.260%   $216.2987   $216.30   $216.30   $216.30  
  Purchase #2 $57.44   3.389%   $59.3866   $59.39   $59.40   $59.40  
  Purchase #3 $47.26   3.410%   $48.8716   $48.87   $48.85   $48.90  
  Purchase #4 $171.28   12.228%   $192.2241   $192.22   $192.20   $192.20  
  Purchase #5 $197.37   9.646%   $216.4083   $216.41   $216.40   $216.40  
  Purchase #6 $33.82   7.200%   $36.255   $36.26   $36.25   $36.30  
  Purchase #7 $224.31   9.737%   $246.1511   $246.15   $246.15   $246.20  
  7 purchase totals = $940.95       $1,015.5954   $1,015.60   $1,015.55   $1,015.70