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 $164.57   13.273%   $186.4134   $186.41   $186.40   $186.40  
  Purchase #2 $89.59   7.132%   $95.9796   $95.98   $96.00   $96.00  
  Purchase #3 $248.48   11.514%   $277.09   $277.09   $277.10   $277.10  
  Purchase #4 $48.75   9.124%   $53.198   $53.20   $53.20   $53.20  
  Purchase #5 $54.85   11.471%   $61.1418   $61.14   $61.15   $61.10  
  Purchase #6 $55.82   13.378%   $63.2876   $63.29   $63.30   $63.30  
  Purchase #7 $10.36   3.854%   $10.7593   $10.76   $10.75   $10.80  
  7 purchase totals = $672.42       $747.8697   $747.87   $747.90   $747.90