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 $43.96   9.331%   $48.0619   $48.06   $48.05   $48.10  
  Purchase #2 $241.95   6.866%   $258.5623   $258.56   $258.55   $258.60  
  Purchase #3 $118.62   5.619%   $125.2853   $125.29   $125.30   $125.30  
  Purchase #4 $241.88   4.200%   $252.039   $252.04   $252.05   $252.00  
  Purchase #5 $64.56   4.685%   $67.5846   $67.58   $67.60   $67.60  
  Purchase #6 $111.85   3.566%   $115.8386   $115.84   $115.85   $115.80  
  Purchase #7 $112.95   5.638%   $119.3181   $119.32   $119.30   $119.30  
  7 purchase totals = $935.77       $986.6898   $986.69   $986.70   $986.70