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 $41.94   3.218%   $43.2896   $43.29   $43.30   $43.30  
  Purchase #2 $77.68   3.793%   $80.6264   $80.63   $80.65   $80.60  
  Purchase #3 $127.81   5.718%   $135.1182   $135.12   $135.10   $135.10  
  Purchase #4 $244.82   13.294%   $277.3664   $277.37   $277.35   $277.40  
  Purchase #5 $135.31   13.573%   $153.6756   $153.68   $153.70   $153.70  
  Purchase #6 $157.47   3.518%   $163.0098   $163.01   $163.00   $163.00  
  Purchase #7 $13.64   4.562%   $14.2623   $14.26   $14.25   $14.30  
  7 purchase totals = $798.67       $867.3483   $867.36   $867.35   $867.40