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 $65.95   5.462%   $69.5522   $69.55   $69.55   $69.60  
  Purchase #2 $5.89   9.603%   $6.4556   $6.46   $6.45   $6.50  
  Purchase #3 $250.34   7.267%   $268.5322   $268.53   $268.55   $268.50  
  Purchase #4 $248.30   6.334%   $264.0273   $264.03   $264.05   $264.00  
  Purchase #5 $250.44   6.646%   $267.0842   $267.08   $267.10   $267.10  
  Purchase #6 $62.48   11.572%   $69.7102   $69.71   $69.70   $69.70  
  Purchase #7 $48.96   13.313%   $55.478   $55.48   $55.50   $55.50  
  7 purchase totals = $932.36       $1,000.8397   $1,000.84   $1,000.90   $1,000.90