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 $185.70   8.252%   $201.024   $201.02   $201.00   $201.00  
  Purchase #2 $51.58   3.176%   $53.2182   $53.22   $53.20   $53.20  
  Purchase #3 $236.83   8.284%   $256.449   $256.45   $256.45   $256.40  
  Purchase #4 $149.47   4.828%   $156.6864   $156.69   $156.70   $156.70  
  Purchase #5 $141.90   12.235%   $159.2615   $159.26   $159.25   $159.30  
  Purchase #6 $80.94   7.263%   $86.8187   $86.82   $86.80   $86.80  
  Purchase #7 $87.29   11.844%   $97.6286   $97.63   $97.65   $97.60  
  7 purchase totals = $933.71       $1,011.0864   $1,011.09   $1,011.05   $1,011.00