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 $60.81   13.341%   $68.9227   $68.92   $68.90   $68.90  
  Purchase #2 $204.60   10.386%   $225.8498   $225.85   $225.85   $225.80  
  Purchase #3 $49.41   8.427%   $53.5738   $53.57   $53.55   $53.60  
  Purchase #4 $155.39   9.514%   $170.1738   $170.17   $170.15   $170.20  
  Purchase #5 $246.53   8.193%   $266.7282   $266.73   $266.75   $266.70  
  Purchase #6 $98.55   8.239%   $106.6695   $106.67   $106.65   $106.70  
  Purchase #7 $72.74   13.629%   $82.6537   $82.65   $82.65   $82.70  
  7 purchase totals = $888.03       $974.5715   $974.56   $974.50   $974.60