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 $57.84   6.812%   $61.7801   $61.78   $61.80   $61.80  
  Purchase #2 $119.87   13.114%   $135.5898   $135.59   $135.60   $135.60  
  Purchase #3 $72.60   5.568%   $76.6424   $76.64   $76.65   $76.60  
  Purchase #4 $173.31   11.381%   $193.0344   $193.03   $193.05   $193.00  
  Purchase #5 $232.80   7.394%   $250.0132   $250.01   $250.00   $250.00  
  Purchase #6 $170.33   4.453%   $177.9148   $177.91   $177.90   $177.90  
  Purchase #7 $157.42   10.401%   $173.7933   $173.79   $173.80   $173.80  
  7 purchase totals = $984.17       $1,068.7680   $1,068.75   $1,068.80   $1,068.70