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 $231.63   6.169%   $245.9193   $245.92   $245.90   $245.90  
  Purchase #2 $204.73   13.136%   $231.6233   $231.62   $231.60   $231.60  
  Purchase #3 $158.99   7.798%   $171.388   $171.39   $171.40   $171.40  
  Purchase #4 $146.92   4.492%   $153.5196   $153.52   $153.50   $153.50  
  Purchase #5 $112.81   6.645%   $120.3062   $120.31   $120.30   $120.30  
  Purchase #6 $219.85   12.220%   $246.7157   $246.72   $246.70   $246.70  
  Purchase #7 $206.45   4.238%   $215.1994   $215.20   $215.20   $215.20  
  7 purchase totals = $1,281.38       $1,384.6715   $1,384.68   $1,384.60   $1,384.60