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 $190.70   4.598%   $199.4684   $199.47   $199.45   $199.50  
  Purchase #2 $8.50   3.645%   $8.8098   $8.81   $8.80   $8.80  
  Purchase #3 $157.72   5.676%   $166.6722   $166.67   $166.65   $166.70  
  Purchase #4 $198.25   11.117%   $220.2895   $220.29   $220.30   $220.30  
  Purchase #5 $28.60   5.780%   $30.2531   $30.25   $30.25   $30.30  
  Purchase #6 $110.46   11.388%   $123.0392   $123.04   $123.05   $123.00  
  Purchase #7 $92.31   9.144%   $100.7508   $100.75   $100.75   $100.80  
  7 purchase totals = $786.54       $849.2830   $849.28   $849.25   $849.40