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 $194.85   4.208%   $203.0493   $203.05   $203.05   $203.00  
  Purchase #2 $66.28   10.558%   $73.2778   $73.28   $73.30   $73.30  
  Purchase #3 $38.49   6.179%   $40.8683   $40.87   $40.85   $40.90  
  Purchase #4 $230.65   11.741%   $257.7306   $257.73   $257.75   $257.70  
  Purchase #5 $164.38   4.229%   $171.3316   $171.33   $171.35   $171.30  
  Purchase #6 $49.58   9.318%   $54.1999   $54.20   $54.20   $54.20  
  Purchase #7 $130.68   11.579%   $145.8114   $145.81   $145.80   $145.80  
  7 purchase totals = $874.91       $946.2689   $946.27   $946.30   $946.20