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 $217.91   12.410%   $244.9526   $244.95   $244.95   $245.00  
  Purchase #2 $180.73   12.821%   $203.9014   $203.90   $203.90   $203.90  
  Purchase #3 $164.65   6.797%   $175.8413   $175.84   $175.85   $175.80  
  Purchase #4 $51.90   13.250%   $58.7768   $58.78   $58.80   $58.80  
  Purchase #5 $97.28   10.743%   $107.7308   $107.73   $107.75   $107.70  
  Purchase #6 $67.76   3.727%   $70.2854   $70.29   $70.30   $70.30  
  Purchase #7 $96.90   9.266%   $105.8788   $105.88   $105.90   $105.90  
  7 purchase totals = $877.13       $967.3671   $967.37   $967.45   $967.40