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 $183.82   13.670%   $208.9482   $208.95   $208.95   $208.90  
  Purchase #2 $186.98   8.745%   $203.3314   $203.33   $203.35   $203.30  
  Purchase #3 $72.51   10.851%   $80.3781   $80.38   $80.40   $80.40  
  Purchase #4 $68.57   12.576%   $77.1934   $77.19   $77.20   $77.20  
  Purchase #5 $108.97   9.799%   $119.648   $119.65   $119.65   $119.60  
  Purchase #6 $85.80   9.651%   $94.0806   $94.08   $94.10   $94.10  
  Purchase #7 $175.29   8.489%   $190.1704   $190.17   $190.15   $190.20  
  7 purchase totals = $881.94       $973.7501   $973.75   $973.80   $973.70