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 $145.96   8.113%   $157.8017   $157.80   $157.80   $157.80  
  Purchase #2 $56.68   10.562%   $62.6665   $62.67   $62.65   $62.70  
  Purchase #3 $151.32   8.538%   $164.2397   $164.24   $164.25   $164.20  
  Purchase #4 $222.81   13.592%   $253.0943   $253.09   $253.10   $253.10  
  Purchase #5 $133.53   3.130%   $137.7095   $137.71   $137.70   $137.70  
  Purchase #6 $14.95   9.231%   $16.33   $16.33   $16.35   $16.30  
  Purchase #7 $31.83   7.835%   $34.3239   $34.32   $34.30   $34.30  
  7 purchase totals = $757.08       $826.1656   $826.16   $826.15   $826.10