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 $56.43   6.818%   $60.2774   $60.28   $60.30   $60.30  
  Purchase #2 $244.58   12.610%   $275.4215   $275.42   $275.40   $275.40  
  Purchase #3 $174.42   3.775%   $181.0044   $181.00   $181.00   $181.00  
  Purchase #4 $66.47   4.182%   $69.2498   $69.25   $69.25   $69.20  
  Purchase #5 $208.61   11.537%   $232.6773   $232.68   $232.70   $232.70  
  Purchase #6 $185.76   10.777%   $205.7794   $205.78   $205.80   $205.80  
  Purchase #7 $205.28   12.723%   $231.3978   $231.40   $231.40   $231.40  
  7 purchase totals = $1,141.55       $1,255.8076   $1,255.81   $1,255.85   $1,255.80