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 $55.31   9.142%   $60.3664   $60.37   $60.35   $60.40  
  Purchase #2 $241.57   6.551%   $257.3953   $257.40   $257.40   $257.40  
  Purchase #3 $206.91   3.779%   $214.7291   $214.73   $214.75   $214.70  
  Purchase #4 $137.99   10.295%   $152.1961   $152.20   $152.20   $152.20  
  Purchase #5 $212.87   5.705%   $225.0142   $225.01   $225.00   $225.00  
  Purchase #6 $169.55   12.838%   $191.3168   $191.32   $191.30   $191.30  
  Purchase #7 $214.93   6.564%   $229.038   $229.04   $229.05   $229.00  
  7 purchase totals = $1,239.13       $1,330.0559   $1,330.07   $1,330.05   $1,330.00