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 $195.94   10.279%   $216.0807   $216.08   $216.10   $216.10  
  Purchase #2 $32.25   6.214%   $34.254   $34.25   $34.25   $34.30  
  Purchase #3 $56.29   3.343%   $58.1718   $58.17   $58.15   $58.20  
  Purchase #4 $187.97   9.816%   $206.4211   $206.42   $206.40   $206.40  
  Purchase #5 $81.62   3.792%   $84.715   $84.72   $84.70   $84.70  
  Purchase #6 $231.85   13.378%   $262.8669   $262.87   $262.85   $262.90  
  Purchase #7 $177.85   5.649%   $187.8967   $187.90   $187.90   $187.90  
  7 purchase totals = $963.77       $1,050.4062   $1,050.41   $1,050.35   $1,050.50