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 $68.58   13.378%   $77.7546   $77.75   $77.75   $77.80  
  Purchase #2 $188.92   8.403%   $204.7949   $204.79   $204.80   $204.80  
  Purchase #3 $47.96   12.308%   $53.8629   $53.86   $53.85   $53.90  
  Purchase #4 $58.34   8.232%   $63.1425   $63.14   $63.15   $63.10  
  Purchase #5 $26.74   11.222%   $29.7408   $29.74   $29.75   $29.70  
  Purchase #6 $165.98   5.137%   $174.5064   $174.51   $174.50   $174.50  
  Purchase #7 $145.42   9.188%   $158.7812   $158.78   $158.80   $158.80  
  7 purchase totals = $701.94       $762.5833   $762.57   $762.60   $762.60