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 $126.93   5.822%   $134.3199   $134.32   $134.30   $134.30  
  Purchase #2 $99.41   6.280%   $105.6529   $105.65   $105.65   $105.70  
  Purchase #3 $44.62   12.440%   $50.1707   $50.17   $50.15   $50.20  
  Purchase #4 $47.86   5.430%   $50.4588   $50.46   $50.45   $50.50  
  Purchase #5 $205.53   10.288%   $226.6749   $226.67   $226.65   $226.70  
  Purchase #6 $48.92   12.611%   $55.0893   $55.09   $55.10   $55.10  
  Purchase #7 $101.87   6.438%   $108.4284   $108.43   $108.45   $108.40  
  7 purchase totals = $675.14       $730.7949   $730.79   $730.75   $730.90