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 $147.60   4.378%   $154.0619   $154.06   $154.05   $154.10  
  Purchase #2 $117.51   6.425%   $125.06   $125.06   $125.05   $125.10  
  Purchase #3 $5.81   13.824%   $6.6132   $6.61   $6.60   $6.60  
  Purchase #4 $247.25   6.438%   $263.168   $263.17   $263.15   $263.20  
  Purchase #5 $117.74   8.142%   $127.3264   $127.33   $127.35   $127.30  
  Purchase #6 $117.28   4.805%   $122.9153   $122.92   $122.90   $122.90  
  Purchase #7 $134.96   6.443%   $143.6555   $143.66   $143.65   $143.70  
  7 purchase totals = $888.15       $942.8003   $942.81   $942.75   $942.90