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 $83.43   11.233%   $92.8017   $92.80   $92.80   $92.80  
  Purchase #2 $69.84   10.326%   $77.0517   $77.05   $77.05   $77.10  
  Purchase #3 $30.67   11.471%   $34.1882   $34.19   $34.20   $34.20  
  Purchase #4 $44.66   6.376%   $47.5075   $47.51   $47.50   $47.50  
  Purchase #5 $38.35   12.213%   $43.0337   $43.03   $43.05   $43.00  
  Purchase #6 $193.39   4.219%   $201.5491   $201.55   $201.55   $201.50  
  Purchase #7 $172.97   6.864%   $184.8427   $184.84   $184.85   $184.80  
  7 purchase totals = $633.31       $680.9746   $680.97   $681.00   $680.90