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 $241.84   3.584%   $250.5075   $250.51   $250.50   $250.50  
  Purchase #2 $195.86   11.409%   $218.2057   $218.21   $218.20   $218.20  
  Purchase #3 $167.62   6.370%   $178.2974   $178.30   $178.30   $178.30  
  Purchase #4 $68.57   13.677%   $77.9483   $77.95   $77.95   $77.90  
  Purchase #5 $205.64   13.451%   $233.3006   $233.30   $233.30   $233.30  
  Purchase #6 $186.29   4.397%   $194.4812   $194.48   $194.50   $194.50  
  Purchase #7 $11.44   12.754%   $12.8991   $12.90   $12.90   $12.90  
  7 purchase totals = $1,077.26       $1,165.6398   $1,165.65   $1,165.65   $1,165.60