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 $52.53   7.143%   $56.2822   $56.28   $56.30   $56.30  
  Purchase #2 $220.95   3.617%   $228.9418   $228.94   $228.95   $228.90  
  Purchase #3 $104.36   5.803%   $110.416   $110.42   $110.40   $110.40  
  Purchase #4 $197.89   8.397%   $214.5068   $214.51   $214.50   $214.50  
  Purchase #5 $35.84   4.564%   $37.4757   $37.48   $37.50   $37.50  
  Purchase #6 $235.99   5.810%   $249.701   $249.70   $249.70   $249.70  
  Purchase #7 $205.88   9.592%   $225.628   $225.63   $225.65   $225.60  
  7 purchase totals = $1,053.44       $1,122.9515   $1,122.96   $1,123.00   $1,122.90