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 $198.94   3.642%   $206.1854   $206.19   $206.20   $206.20  
  Purchase #2 $184.92   4.337%   $192.94   $192.94   $192.95   $192.90  
  Purchase #3 $144.42   13.359%   $163.7131   $163.71   $163.70   $163.70  
  Purchase #4 $216.39   7.371%   $232.3401   $232.34   $232.35   $232.30  
  Purchase #5 $247.77   3.121%   $255.5029   $255.50   $255.50   $255.50  
  Purchase #6 $182.25   11.827%   $203.8047   $203.80   $203.80   $203.80  
  Purchase #7 $118.66   6.733%   $126.6494   $126.65   $126.65   $126.60  
  7 purchase totals = $1,293.35       $1,381.1356   $1,381.13   $1,381.15   $1,381.00