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 $56.35   7.864%   $60.7814   $60.78   $60.80   $60.80  
  Purchase #2 $53.84   8.432%   $58.3798   $58.38   $58.40   $58.40  
  Purchase #3 $219.53   7.435%   $235.8521   $235.85   $235.85   $235.90  
  Purchase #4 $50.69   13.166%   $57.3638   $57.36   $57.35   $57.40  
  Purchase #5 $129.68   10.252%   $142.9748   $142.97   $142.95   $143.00  
  Purchase #6 $244.37   6.185%   $259.4843   $259.48   $259.50   $259.50  
  Purchase #7 $230.27   7.159%   $246.755   $246.76   $246.75   $246.80  
  7 purchase totals = $984.73       $1,061.5912   $1,061.58   $1,061.60   $1,061.80