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 $41.51   12.554%   $46.7212   $46.72   $46.70   $46.70  
  Purchase #2 $189.44   8.629%   $205.7868   $205.79   $205.80   $205.80  
  Purchase #3 $249.80   9.525%   $273.5935   $273.59   $273.60   $273.60  
  Purchase #4 $206.68   9.517%   $226.3497   $226.35   $226.35   $226.30  
  Purchase #5 $117.83   13.477%   $133.7099   $133.71   $133.70   $133.70  
  Purchase #6 $242.60   6.814%   $259.1308   $259.13   $259.15   $259.10  
  Purchase #7 $136.81   12.225%   $153.535   $153.54   $153.55   $153.50  
  7 purchase totals = $1,184.67       $1,298.8269   $1,298.83   $1,298.85   $1,298.70