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 $12.66   3.712%   $13.1299   $13.13   $13.15   $13.10  
  Purchase #2 $78.65   4.457%   $82.1554   $82.16   $82.15   $82.20  
  Purchase #3 $146.29   6.319%   $155.5341   $155.53   $155.55   $155.50  
  Purchase #4 $51.63   10.713%   $57.1611   $57.16   $57.15   $57.20  
  Purchase #5 $165.33   7.505%   $177.738   $177.74   $177.75   $177.70  
  Purchase #6 $69.70   4.274%   $72.679   $72.68   $72.70   $72.70  
  Purchase #7 $178.27   10.871%   $197.6497   $197.65   $197.65   $197.60  
  7 purchase totals = $702.53       $756.0472   $756.05   $756.10   $756.00