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 $204.65   6.851%   $218.6706   $218.67   $218.65   $218.70  
  Purchase #2 $131.81   9.245%   $143.9958   $144.00   $144.00   $144.00  
  Purchase #3 $134.65   7.645%   $144.944   $144.94   $144.95   $144.90  
  Purchase #4 $134.40   5.732%   $142.1038   $142.10   $142.10   $142.10  
  Purchase #5 $164.96   13.114%   $186.5929   $186.59   $186.60   $186.60  
  Purchase #6 $223.72   13.691%   $254.3495   $254.35   $254.35   $254.30  
  Purchase #7 $245.58   9.221%   $268.2249   $268.22   $268.20   $268.20  
  7 purchase totals = $1,239.77       $1,358.8815   $1,358.87   $1,358.85   $1,358.80