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 $60.56   13.834%   $68.9379   $68.94   $68.95   $68.90  
  Purchase #2 $15.62   8.233%   $16.906   $16.91   $16.90   $16.90  
  Purchase #3 $39.36   7.534%   $42.3254   $42.33   $42.35   $42.30  
  Purchase #4 $250.71   7.512%   $269.5433   $269.54   $269.55   $269.50  
  Purchase #5 $249.30   7.473%   $267.9302   $267.93   $267.95   $267.90  
  Purchase #6 $127.67   13.475%   $144.8735   $144.87   $144.85   $144.90  
  Purchase #7 $203.94   6.112%   $216.4048   $216.40   $216.40   $216.40  
  7 purchase totals = $947.16       $1,026.9211   $1,026.92   $1,026.95   $1,026.80