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 $34.73   6.368%   $36.9416   $36.94   $36.95   $36.90  
  Purchase #2 $222.59   8.422%   $241.3365   $241.34   $241.35   $241.30  
  Purchase #3 $29.82   6.610%   $31.7911   $31.79   $31.80   $31.80  
  Purchase #4 $98.51   11.113%   $109.4574   $109.46   $109.45   $109.50  
  Purchase #5 $208.80   8.272%   $226.0719   $226.07   $226.05   $226.10  
  Purchase #6 $227.38   10.651%   $251.5982   $251.60   $251.60   $251.60  
  Purchase #7 $170.25   3.543%   $176.282   $176.28   $176.30   $176.30  
  7 purchase totals = $992.08       $1,073.4787   $1,073.48   $1,073.50   $1,073.50