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 $160.86   9.857%   $176.716   $176.72   $176.70   $176.70  
  Purchase #2 $25.75   3.664%   $26.6935   $26.69   $26.70   $26.70  
  Purchase #3 $244.87   9.713%   $268.6542   $268.65   $268.65   $268.70  
  Purchase #4 $93.83   7.651%   $101.0089   $101.01   $101.00   $101.00  
  Purchase #5 $129.56   6.710%   $138.2535   $138.25   $138.25   $138.30  
  Purchase #6 $172.33   5.423%   $181.6755   $181.68   $181.70   $181.70  
  Purchase #7 $214.65   9.304%   $234.621   $234.62   $234.60   $234.60  
  7 purchase totals = $1,041.85       $1,127.6226   $1,127.62   $1,127.60   $1,127.70