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 $177.77   8.590%   $193.0404   $193.04   $193.05   $193.00  
  Purchase #2 $160.62   8.673%   $174.5506   $174.55   $174.55   $174.60  
  Purchase #3 $103.44   6.614%   $110.2815   $110.28   $110.30   $110.30  
  Purchase #4 $43.83   9.270%   $47.893   $47.89   $47.90   $47.90  
  Purchase #5 $29.85   8.157%   $32.2849   $32.28   $32.30   $32.30  
  Purchase #6 $119.93   13.671%   $136.3256   $136.33   $136.35   $136.30  
  Purchase #7 $237.49   6.684%   $253.3638   $253.36   $253.35   $253.40  
  7 purchase totals = $872.93       $947.7398   $947.73   $947.80   $947.80