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 $81.63   13.825%   $92.9153   $92.92   $92.90   $92.90  
  Purchase #2 $168.98   6.423%   $179.8336   $179.83   $179.85   $179.80  
  Purchase #3 $203.55   6.421%   $216.6199   $216.62   $216.60   $216.60  
  Purchase #4 $135.87   9.707%   $149.0589   $149.06   $149.05   $149.10  
  Purchase #5 $214.37   7.796%   $231.0823   $231.08   $231.10   $231.10  
  Purchase #6 $225.41   9.255%   $246.2717   $246.27   $246.25   $246.30  
  Purchase #7 $97.98   5.614%   $103.4806   $103.48   $103.50   $103.50  
  7 purchase totals = $1,127.79       $1,219.2623   $1,219.26   $1,219.25   $1,219.30