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 $204.58   8.114%   $221.1796   $221.18   $221.20   $221.20  
  Purchase #2 $57.96   13.796%   $65.9562   $65.96   $65.95   $66.00  
  Purchase #3 $51.69   6.505%   $55.0524   $55.05   $55.05   $55.10  
  Purchase #4 $120.42   12.835%   $135.8759   $135.88   $135.90   $135.90  
  Purchase #5 $130.53   9.533%   $142.9734   $142.97   $142.95   $143.00  
  Purchase #6 $60.53   12.409%   $68.0412   $68.04   $68.05   $68.00  
  Purchase #7 $62.33   8.799%   $67.8144   $67.81   $67.80   $67.80  
  7 purchase totals = $688.04       $756.8931   $756.89   $756.90   $757.00