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 $181.30   12.497%   $203.9571   $203.96   $203.95   $204.00  
  Purchase #2 $54.71   3.739%   $56.7556   $56.76   $56.75   $56.80  
  Purchase #3 $44.54   5.762%   $47.1064   $47.11   $47.10   $47.10  
  Purchase #4 $70.85   10.187%   $78.0675   $78.07   $78.05   $78.10  
  Purchase #5 $105.25   13.773%   $119.7461   $119.75   $119.75   $119.70  
  Purchase #6 $87.77   3.467%   $90.813   $90.81   $90.80   $90.80  
  Purchase #7 $158.87   7.555%   $170.8726   $170.87   $170.85   $170.90  
  7 purchase totals = $703.29       $767.3183   $767.33   $767.25   $767.40