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 $222.70   9.169%   $243.1194   $243.12   $243.10   $243.10  
  Purchase #2 $204.77   4.278%   $213.5301   $213.53   $213.55   $213.50  
  Purchase #3 $201.89   4.764%   $211.508   $211.51   $211.50   $211.50  
  Purchase #4 $242.41   13.467%   $275.0554   $275.06   $275.05   $275.10  
  Purchase #5 $200.66   7.142%   $214.9911   $214.99   $215.00   $215.00  
  Purchase #6 $94.55   9.348%   $103.3885   $103.39   $103.40   $103.40  
  Purchase #7 $60.88   3.833%   $63.2135   $63.21   $63.20   $63.20  
  7 purchase totals = $1,227.86       $1,324.8060   $1,324.81   $1,324.80   $1,324.80