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 $140.93   9.804%   $154.7468   $154.75   $154.75   $154.70  
  Purchase #2 $233.95   13.596%   $265.7578   $265.76   $265.75   $265.80  
  Purchase #3 $55.55   13.373%   $62.9787   $62.98   $63.00   $63.00  
  Purchase #4 $54.35   6.789%   $58.0398   $58.04   $58.05   $58.00  
  Purchase #5 $37.47   9.233%   $40.9296   $40.93   $40.95   $40.90  
  Purchase #6 $118.61   12.369%   $133.2809   $133.28   $133.30   $133.30  
  Purchase #7 $83.93   9.433%   $91.8471   $91.85   $91.85   $91.80  
  7 purchase totals = $724.79       $807.5807   $807.59   $807.65   $807.50