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 $65.35   5.116%   $68.6933   $68.69   $68.70   $68.70  
  Purchase #2 $240.92   4.138%   $250.8893   $250.89   $250.90   $250.90  
  Purchase #3 $190.96   7.220%   $204.7473   $204.75   $204.75   $204.70  
  Purchase #4 $48.72   7.398%   $52.3243   $52.32   $52.30   $52.30  
  Purchase #5 $234.90   5.654%   $248.1812   $248.18   $248.20   $248.20  
  Purchase #6 $173.73   8.772%   $188.9696   $188.97   $188.95   $189.00  
  Purchase #7 $224.80   10.200%   $247.7296   $247.73   $247.75   $247.70  
  7 purchase totals = $1,179.38       $1,261.5346   $1,261.53   $1,261.55   $1,261.50