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 $114.74   3.127%   $118.3279   $118.33   $118.35   $118.30  
  Purchase #2 $52.97   3.225%   $54.6783   $54.68   $54.70   $54.70  
  Purchase #3 $124.64   5.277%   $131.2173   $131.22   $131.20   $131.20  
  Purchase #4 $202.55   6.697%   $216.1148   $216.11   $216.10   $216.10  
  Purchase #5 $224.70   9.563%   $246.1881   $246.19   $246.20   $246.20  
  Purchase #6 $230.36   6.344%   $244.974   $244.97   $244.95   $245.00  
  Purchase #7 $186.87   9.370%   $204.3797   $204.38   $204.40   $204.40  
  7 purchase totals = $1,136.83       $1,215.8801   $1,215.88   $1,215.90   $1,215.90