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 $67.46   12.149%   $75.6557   $75.66   $75.65   $75.70  
  Purchase #2 $112.36   4.759%   $117.7072   $117.71   $117.70   $117.70  
  Purchase #3 $202.84   10.169%   $223.4668   $223.47   $223.45   $223.50  
  Purchase #4 $150.94   7.145%   $161.7247   $161.72   $161.70   $161.70  
  Purchase #5 $186.35   11.390%   $207.5753   $207.58   $207.60   $207.60  
  Purchase #6 $12.68   11.689%   $14.1622   $14.16   $14.15   $14.20  
  Purchase #7 $41.85   11.409%   $46.6247   $46.62   $46.60   $46.60  
  7 purchase totals = $774.48       $846.9166   $846.92   $846.85   $847.00