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 $163.91   13.229%   $185.5937   $185.59   $185.60   $185.60  
  Purchase #2 $126.29   3.128%   $130.2404   $130.24   $130.25   $130.20  
  Purchase #3 $150.54   7.144%   $161.2946   $161.29   $161.30   $161.30  
  Purchase #4 $25.25   7.311%   $27.096   $27.10   $27.10   $27.10  
  Purchase #5 $195.92   9.592%   $214.7126   $214.71   $214.70   $214.70  
  Purchase #6 $182.64   13.457%   $207.2179   $207.22   $207.20   $207.20  
  Purchase #7 $61.96   12.288%   $69.5736   $69.57   $69.55   $69.60  
  7 purchase totals = $906.51       $995.7288   $995.72   $995.70   $995.70