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 $85.84   9.803%   $94.2549   $94.25   $94.25   $94.30  
  Purchase #2 $249.97   11.355%   $278.3541   $278.35   $278.35   $278.40  
  Purchase #3 $51.56   12.397%   $57.9519   $57.95   $57.95   $58.00  
  Purchase #4 $246.57   7.257%   $264.4636   $264.46   $264.45   $264.50  
  Purchase #5 $71.54   7.436%   $76.8597   $76.86   $76.85   $76.90  
  Purchase #6 $154.86   13.104%   $175.1529   $175.15   $175.15   $175.20  
  Purchase #7 $219.68   9.214%   $239.9213   $239.92   $239.90   $239.90  
  7 purchase totals = $1,080.02       $1,186.9584   $1,186.94   $1,186.90   $1,187.20