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 $124.42   7.707%   $134.009   $134.01   $134.00   $134.00  
  Purchase #2 $55.87   12.336%   $62.7621   $62.76   $62.75   $62.80  
  Purchase #3 $241.33   4.172%   $251.3983   $251.40   $251.40   $251.40  
  Purchase #4 $193.45   7.347%   $207.6628   $207.66   $207.65   $207.70  
  Purchase #5 $148.51   8.433%   $161.0338   $161.03   $161.05   $161.00  
  Purchase #6 $196.80   9.171%   $214.8485   $214.85   $214.85   $214.80  
  Purchase #7 $238.48   8.461%   $258.6578   $258.66   $258.65   $258.70  
  7 purchase totals = $1,198.86       $1,290.3723   $1,290.37   $1,290.35   $1,290.40