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 $227.35   10.729%   $251.7424   $251.74   $251.75   $251.70  
  Purchase #2 $116.49   3.772%   $120.884   $120.88   $120.90   $120.90  
  Purchase #3 $169.38   4.389%   $176.8141   $176.81   $176.80   $176.80  
  Purchase #4 $70.62   6.183%   $74.9864   $74.99   $75.00   $75.00  
  Purchase #5 $93.99   6.714%   $100.3005   $100.30   $100.30   $100.30  
  Purchase #6 $46.49   10.498%   $51.3705   $51.37   $51.35   $51.40  
  Purchase #7 $244.95   3.542%   $253.6261   $253.63   $253.65   $253.60  
  7 purchase totals = $969.27       $1,029.7240   $1,029.72   $1,029.75   $1,029.70