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 $61.79   12.102%   $69.2678   $69.27   $69.25   $69.30  
  Purchase #2 $218.47   3.861%   $226.9051   $226.91   $226.90   $226.90  
  Purchase #3 $71.57   3.218%   $73.8731   $73.87   $73.85   $73.90  
  Purchase #4 $51.57   5.227%   $54.2656   $54.27   $54.25   $54.30  
  Purchase #5 $28.67   3.108%   $29.5611   $29.56   $29.55   $29.60  
  Purchase #6 $153.63   8.824%   $167.1863   $167.19   $167.20   $167.20  
  Purchase #7 $182.73   11.460%   $203.6709   $203.67   $203.65   $203.70  
  7 purchase totals = $768.43       $824.7299   $824.74   $824.65   $824.90