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 $233.66   5.866%   $247.3665   $247.37   $247.35   $247.40  
  Purchase #2 $27.95   6.634%   $29.8042   $29.80   $29.80   $29.80  
  Purchase #3 $180.78   11.381%   $201.3546   $201.35   $201.35   $201.40  
  Purchase #4 $130.85   4.222%   $136.3745   $136.37   $136.35   $136.40  
  Purchase #5 $21.32   5.866%   $22.5706   $22.57   $22.55   $22.60  
  Purchase #6 $165.63   11.361%   $184.4472   $184.45   $184.45   $184.40  
  Purchase #7 $211.38   10.449%   $233.4671   $233.47   $233.45   $233.50  
  7 purchase totals = $971.57       $1,055.3847   $1,055.38   $1,055.30   $1,055.50