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 $79.38   4.118%   $82.6489   $82.65   $82.65   $82.60  
  Purchase #2 $192.84   12.178%   $216.3241   $216.32   $216.30   $216.30  
  Purchase #3 $24.51   6.670%   $26.1448   $26.14   $26.15   $26.10  
  Purchase #4 $65.57   6.128%   $69.5881   $69.59   $69.60   $69.60  
  Purchase #5 $55.51   13.135%   $62.8012   $62.80   $62.80   $62.80  
  Purchase #6 $189.97   8.855%   $206.7918   $206.79   $206.80   $206.80  
  Purchase #7 $105.62   9.655%   $115.8176   $115.82   $115.80   $115.80  
  7 purchase totals = $713.40       $780.1165   $780.11   $780.10   $780.00