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 $165.90   11.267%   $184.592   $184.59   $184.60   $184.60  
  Purchase #2 $22.39   7.803%   $24.1371   $24.14   $24.15   $24.10  
  Purchase #3 $118.30   6.280%   $125.7292   $125.73   $125.75   $125.70  
  Purchase #4 $216.83   6.853%   $231.6894   $231.69   $231.70   $231.70  
  Purchase #5 $89.77   7.740%   $96.7182   $96.72   $96.70   $96.70  
  Purchase #6 $246.26   5.716%   $260.3362   $260.34   $260.35   $260.30  
  Purchase #7 $89.40   3.809%   $92.8052   $92.81   $92.80   $92.80  
  7 purchase totals = $948.85       $1,016.0073   $1,016.02   $1,016.05   $1,015.90