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 $146.82   5.828%   $155.3767   $155.38   $155.40   $155.40  
  Purchase #2 $200.67   11.571%   $223.8895   $223.89   $223.90   $223.90  
  Purchase #3 $232.86   5.759%   $246.2704   $246.27   $246.25   $246.30  
  Purchase #4 $236.42   3.127%   $243.8129   $243.81   $243.80   $243.80  
  Purchase #5 $221.80   12.529%   $249.5893   $249.59   $249.60   $249.60  
  Purchase #6 $16.37   7.529%   $17.6025   $17.60   $17.60   $17.60  
  Purchase #7 $38.79   5.772%   $41.029   $41.03   $41.05   $41.00  
  7 purchase totals = $1,093.73       $1,177.5703   $1,177.57   $1,177.60   $1,177.60