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 $92.44   6.395%   $98.3515   $98.35   $98.35   $98.40  
  Purchase #2 $152.95   13.369%   $173.3979   $173.40   $173.40   $173.40  
  Purchase #3 $150.53   3.701%   $156.1011   $156.10   $156.10   $156.10  
  Purchase #4 $189.30   3.198%   $195.3538   $195.35   $195.35   $195.40  
  Purchase #5 $105.29   11.755%   $117.6668   $117.67   $117.65   $117.70  
  Purchase #6 $139.36   12.415%   $156.6615   $156.66   $156.65   $156.70  
  Purchase #7 $142.69   10.866%   $158.1947   $158.19   $158.20   $158.20  
  7 purchase totals = $972.56       $1,055.7273   $1,055.72   $1,055.70   $1,055.90