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 $229.81   3.251%   $237.2811   $237.28   $237.30   $237.30  
  Purchase #2 $178.67   9.211%   $195.1273   $195.13   $195.15   $195.10  
  Purchase #3 $89.99   6.444%   $95.789   $95.79   $95.80   $95.80  
  Purchase #4 $197.75   11.598%   $220.685   $220.69   $220.70   $220.70  
  Purchase #5 $13.57   5.657%   $14.3377   $14.34   $14.35   $14.30  
  Purchase #6 $60.50   6.270%   $64.2934   $64.29   $64.30   $64.30  
  Purchase #7 $175.33   11.539%   $195.5613   $195.56   $195.55   $195.60  
  7 purchase totals = $945.62       $1,023.0748   $1,023.08   $1,023.15   $1,023.10