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 $214.44   12.375%   $240.977   $240.98   $241.00   $241.00  
  Purchase #2 $104.62   4.721%   $109.5591   $109.56   $109.55   $109.60  
  Purchase #3 $233.55   11.346%   $260.0486   $260.05   $260.05   $260.00  
  Purchase #4 $167.59   3.433%   $173.3434   $173.34   $173.35   $173.30  
  Purchase #5 $51.37   9.730%   $56.3683   $56.37   $56.35   $56.40  
  Purchase #6 $206.92   11.583%   $230.8875   $230.89   $230.90   $230.90  
  Purchase #7 $50.84   6.281%   $54.0333   $54.03   $54.05   $54.00  
  7 purchase totals = $1,029.33       $1,125.2172   $1,125.22   $1,125.25   $1,125.20