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 $53.31   9.711%   $58.4869   $58.49   $58.50   $58.50  
  Purchase #2 $202.41   11.562%   $225.8126   $225.81   $225.80   $225.80  
  Purchase #3 $249.31   7.253%   $267.3925   $267.39   $267.40   $267.40  
  Purchase #4 $59.65   11.759%   $66.6642   $66.66   $66.65   $66.70  
  Purchase #5 $197.71   3.149%   $203.9359   $203.94   $203.95   $203.90  
  Purchase #6 $119.69   3.259%   $123.5907   $123.59   $123.60   $123.60  
  Purchase #7 $247.72   10.607%   $273.9957   $274.00   $274.00   $274.00  
  7 purchase totals = $1,129.80       $1,219.8785   $1,219.88   $1,219.90   $1,219.90