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 $187.77   8.239%   $203.2404   $203.24   $203.25   $203.20  
  Purchase #2 $247.86   10.308%   $273.4094   $273.41   $273.40   $273.40  
  Purchase #3 $217.76   5.623%   $230.0046   $230.00   $230.00   $230.00  
  Purchase #4 $246.74   5.592%   $260.5377   $260.54   $260.55   $260.50  
  Purchase #5 $216.68   11.777%   $242.1984   $242.20   $242.20   $242.20  
  Purchase #6 $86.91   9.799%   $95.4263   $95.43   $95.45   $95.40  
  Purchase #7 $166.27   3.128%   $171.4709   $171.47   $171.45   $171.50  
  7 purchase totals = $1,369.99       $1,476.2877   $1,476.29   $1,476.30   $1,476.20