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 $207.95   10.818%   $230.446   $230.45   $230.45   $230.40  
  Purchase #2 $26.63   12.472%   $29.9513   $29.95   $29.95   $30.00  
  Purchase #3 $206.73   9.548%   $226.4686   $226.47   $226.45   $226.50  
  Purchase #4 $45.86   6.515%   $48.8478   $48.85   $48.85   $48.80  
  Purchase #5 $150.92   9.310%   $164.9707   $164.97   $164.95   $165.00  
  Purchase #6 $46.25   7.495%   $49.7164   $49.72   $49.70   $49.70  
  Purchase #7 $237.40   5.823%   $251.2238   $251.22   $251.20   $251.20  
  7 purchase totals = $921.74       $1,001.6246   $1,001.63   $1,001.55   $1,001.60