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 $181.88   12.438%   $204.5022   $204.50   $204.50   $204.50  
  Purchase #2 $101.31   11.754%   $113.218   $113.22   $113.20   $113.20  
  Purchase #3 $119.37   4.122%   $124.2904   $124.29   $124.30   $124.30  
  Purchase #4 $196.98   9.451%   $215.5966   $215.60   $215.60   $215.60  
  Purchase #5 $40.31   3.293%   $41.6374   $41.64   $41.65   $41.60  
  Purchase #6 $193.70   11.750%   $216.4598   $216.46   $216.45   $216.50  
  Purchase #7 $160.77   10.719%   $178.0029   $178.00   $178.00   $178.00  
  7 purchase totals = $994.32       $1,093.7073   $1,093.71   $1,093.70   $1,093.70