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 $184.55   12.169%   $207.0079   $207.01   $207.00   $207.00  
  Purchase #2 $225.62   7.127%   $241.6999   $241.70   $241.70   $241.70  
  Purchase #3 $16.55   11.800%   $18.5029   $18.50   $18.50   $18.50  
  Purchase #4 $246.82   3.320%   $255.0144   $255.01   $255.00   $255.00  
  Purchase #5 $64.54   3.409%   $66.7402   $66.74   $66.75   $66.70  
  Purchase #6 $5.27   12.386%   $5.9227   $5.92   $5.90   $5.90  
  Purchase #7 $172.41   8.659%   $187.339   $187.34   $187.35   $187.30  
  7 purchase totals = $915.76       $982.2270   $982.22   $982.20   $982.10