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 $58.84   11.644%   $65.6913   $65.69   $65.70   $65.70  
  Purchase #2 $198.31   10.754%   $219.6363   $219.64   $219.65   $219.60  
  Purchase #3 $191.26   12.831%   $215.8006   $215.80   $215.80   $215.80  
  Purchase #4 $72.27   5.116%   $75.9673   $75.97   $75.95   $76.00  
  Purchase #5 $155.68   13.768%   $177.114   $177.11   $177.10   $177.10  
  Purchase #6 $32.33   6.659%   $34.4829   $34.48   $34.50   $34.50  
  Purchase #7 $209.30   4.292%   $218.2832   $218.28   $218.30   $218.30  
  7 purchase totals = $917.99       $1,006.9756   $1,006.97   $1,007.00   $1,007.00