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 $91.61   4.803%   $96.01   $96.01   $96.00   $96.00  
  Purchase #2 $60.31   9.605%   $66.1028   $66.10   $66.10   $66.10  
  Purchase #3 $133.86   4.524%   $139.9158   $139.92   $139.90   $139.90  
  Purchase #4 $21.52   5.549%   $22.7141   $22.71   $22.70   $22.70  
  Purchase #5 $240.98   12.199%   $270.3772   $270.38   $270.40   $270.40  
  Purchase #6 $197.40   8.104%   $213.3973   $213.40   $213.40   $213.40  
  Purchase #7 $189.25   7.248%   $202.9668   $202.97   $202.95   $203.00  
  7 purchase totals = $934.93       $1,011.4840   $1,011.49   $1,011.45   $1,011.50