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 $71.27   3.497%   $73.7623   $73.76   $73.75   $73.80  
  Purchase #2 $176.83   13.536%   $200.7657   $200.77   $200.75   $200.80  
  Purchase #3 $223.81   13.293%   $253.5611   $253.56   $253.55   $253.60  
  Purchase #4 $213.27   7.847%   $230.0053   $230.01   $230.00   $230.00  
  Purchase #5 $231.47   8.124%   $250.2746   $250.27   $250.25   $250.30  
  Purchase #6 $6.95   12.784%   $7.8385   $7.84   $7.85   $7.80  
  Purchase #7 $125.77   7.373%   $135.043   $135.04   $135.05   $135.00  
  7 purchase totals = $1,049.37       $1,151.2505   $1,151.25   $1,151.20   $1,151.30