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 $216.97   5.405%   $228.6972   $228.70   $228.70   $228.70  
  Purchase #2 $75.39   3.210%   $77.81   $77.81   $77.80   $77.80  
  Purchase #3 $30.47   10.560%   $33.6876   $33.69   $33.70   $33.70  
  Purchase #4 $242.84   5.196%   $255.458   $255.46   $255.45   $255.50  
  Purchase #5 $113.64   8.853%   $123.7005   $123.70   $123.70   $123.70  
  Purchase #6 $5.34   11.449%   $5.9514   $5.95   $5.95   $6.00  
  Purchase #7 $248.42   11.512%   $277.0181   $277.02   $277.00   $277.00  
  7 purchase totals = $933.07       $1,002.3228   $1,002.33   $1,002.30   $1,002.40