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 $236.76   6.331%   $251.7493   $251.75   $251.75   $251.70  
  Purchase #2 $51.49   9.786%   $56.5288   $56.53   $56.55   $56.50  
  Purchase #3 $157.76   4.809%   $165.3467   $165.35   $165.35   $165.30  
  Purchase #4 $17.93   5.320%   $18.8839   $18.88   $18.90   $18.90  
  Purchase #5 $204.60   9.274%   $223.5746   $223.57   $223.55   $223.60  
  Purchase #6 $193.66   10.352%   $213.7077   $213.71   $213.70   $213.70  
  Purchase #7 $146.63   4.610%   $153.3896   $153.39   $153.40   $153.40  
  7 purchase totals = $1,008.83       $1,083.1806   $1,083.18   $1,083.20   $1,083.10