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 $111.29   13.593%   $126.4176   $126.42   $126.40   $126.40  
  Purchase #2 $197.63   3.557%   $204.6597   $204.66   $204.65   $204.70  
  Purchase #3 $195.37   13.816%   $222.3623   $222.36   $222.35   $222.40  
  Purchase #4 $195.57   4.149%   $203.6842   $203.68   $203.70   $203.70  
  Purchase #5 $97.51   9.712%   $106.9802   $106.98   $107.00   $107.00  
  Purchase #6 $213.60   4.716%   $223.6734   $223.67   $223.65   $223.70  
  Purchase #7 $224.86   4.715%   $235.4621   $235.46   $235.45   $235.50  
  7 purchase totals = $1,235.83       $1,323.2395   $1,323.23   $1,323.20   $1,323.40