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 $185.99   10.213%   $204.9852   $204.99   $205.00   $205.00  
  Purchase #2 $210.28   9.187%   $229.5984   $229.60   $229.60   $229.60  
  Purchase #3 $235.59   12.556%   $265.1707   $265.17   $265.15   $265.20  
  Purchase #4 $26.25   5.238%   $27.625   $27.63   $27.65   $27.60  
  Purchase #5 $71.49   5.227%   $75.2268   $75.23   $75.25   $75.20  
  Purchase #6 $55.92   6.779%   $59.7108   $59.71   $59.70   $59.70  
  Purchase #7 $133.59   5.607%   $141.0804   $141.08   $141.10   $141.10  
  7 purchase totals = $919.11       $1,003.3973   $1,003.41   $1,003.45   $1,003.40