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 $68.67   7.371%   $73.7317   $73.73   $73.75   $73.70  
  Purchase #2 $44.74   11.182%   $49.7428   $49.74   $49.75   $49.70  
  Purchase #3 $212.68   13.749%   $241.9214   $241.92   $241.90   $241.90  
  Purchase #4 $29.72   4.779%   $31.1403   $31.14   $31.15   $31.10  
  Purchase #5 $239.39   13.354%   $271.3581   $271.36   $271.35   $271.40  
  Purchase #6 $212.53   12.110%   $238.2674   $238.27   $238.25   $238.30  
  Purchase #7 $113.64   13.102%   $128.5291   $128.53   $128.55   $128.50  
  7 purchase totals = $921.37       $1,034.6908   $1,034.69   $1,034.70   $1,034.60