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 $120.76   4.137%   $125.7558   $125.76   $125.75   $125.80  
  Purchase #2 $238.31   12.406%   $267.8747   $267.87   $267.85   $267.90  
  Purchase #3 $106.48   13.436%   $120.7867   $120.79   $120.80   $120.80  
  Purchase #4 $198.67   3.570%   $205.7625   $205.76   $205.75   $205.80  
  Purchase #5 $143.76   9.534%   $157.4661   $157.47   $157.45   $157.50  
  Purchase #6 $117.34   12.175%   $131.6261   $131.63   $131.65   $131.60  
  Purchase #7 $15.37   11.558%   $17.1465   $17.15   $17.15   $17.10  
  7 purchase totals = $940.69       $1,026.4184   $1,026.43   $1,026.40   $1,026.50