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 $39.79   11.586%   $44.4001   $44.40   $44.40   $44.40  
  Purchase #2 $6.33   12.347%   $7.1116   $7.11   $7.10   $7.10  
  Purchase #3 $21.67   8.774%   $23.5713   $23.57   $23.55   $23.60  
  Purchase #4 $248.40   7.723%   $267.5839   $267.58   $267.60   $267.60  
  Purchase #5 $151.71   10.480%   $167.6092   $167.61   $167.60   $167.60  
  Purchase #6 $24.60   7.670%   $26.4868   $26.49   $26.50   $26.50  
  Purchase #7 $212.97   5.274%   $224.202   $224.20   $224.20   $224.20  
  7 purchase totals = $705.47       $760.9649   $760.96   $760.95   $761.00