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 $194.89   5.864%   $206.3183   $206.32   $206.30   $206.30  
  Purchase #2 $32.43   11.207%   $36.0644   $36.06   $36.05   $36.10  
  Purchase #3 $236.94   8.272%   $256.5397   $256.54   $256.55   $256.50  
  Purchase #4 $174.34   11.298%   $194.0369   $194.04   $194.05   $194.00  
  Purchase #5 $241.29   3.518%   $249.7786   $249.78   $249.80   $249.80  
  Purchase #6 $21.57   8.525%   $23.4088   $23.41   $23.40   $23.40  
  Purchase #7 $82.50   4.812%   $86.4699   $86.47   $86.45   $86.50  
  7 purchase totals = $983.96       $1,052.6166   $1,052.62   $1,052.60   $1,052.60