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 $124.56   8.355%   $134.967   $134.97   $134.95   $135.00  
  Purchase #2 $79.40   7.183%   $85.1033   $85.10   $85.10   $85.10  
  Purchase #3 $95.87   12.730%   $108.0743   $108.07   $108.05   $108.10  
  Purchase #4 $165.69   5.176%   $174.2661   $174.27   $174.25   $174.30  
  Purchase #5 $210.99   6.362%   $224.4132   $224.41   $224.40   $224.40  
  Purchase #6 $115.67   8.277%   $125.244   $125.24   $125.25   $125.20  
  Purchase #7 $158.72   5.121%   $166.8481   $166.85   $166.85   $166.80  
  7 purchase totals = $950.90       $1,018.9160   $1,018.91   $1,018.85   $1,018.90