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 $70.32   10.262%   $77.5362   $77.54   $77.55   $77.50  
  Purchase #2 $153.97   8.231%   $166.6433   $166.64   $166.65   $166.60  
  Purchase #3 $5.63   7.376%   $6.0453   $6.05   $6.05   $6.00  
  Purchase #4 $96.51   7.461%   $103.7106   $103.71   $103.70   $103.70  
  Purchase #5 $69.94   4.302%   $72.9488   $72.95   $72.95   $72.90  
  Purchase #6 $12.59   7.765%   $13.5676   $13.57   $13.55   $13.60  
  Purchase #7 $211.29   5.584%   $223.0884   $223.09   $223.10   $223.10  
  7 purchase totals = $620.25       $663.5402   $663.55   $663.55   $663.40