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 $69.44   5.744%   $73.4286   $73.43   $73.45   $73.40  
  Purchase #2 $44.92   5.109%   $47.215   $47.22   $47.20   $47.20  
  Purchase #3 $184.64   13.623%   $209.7935   $209.79   $209.80   $209.80  
  Purchase #4 $207.27   11.285%   $230.6604   $230.66   $230.65   $230.70  
  Purchase #5 $239.67   4.814%   $251.2077   $251.21   $251.20   $251.20  
  Purchase #6 $49.92   11.169%   $55.4956   $55.50   $55.50   $55.50  
  Purchase #7 $126.86   5.628%   $133.9997   $134.00   $134.00   $134.00  
  7 purchase totals = $922.72       $1,001.8005   $1,001.81   $1,001.80   $1,001.80