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 $134.75   8.159%   $145.7443   $145.74   $145.75   $145.70  
  Purchase #2 $226.84   10.307%   $250.2204   $250.22   $250.20   $250.20  
  Purchase #3 $169.87   5.789%   $179.7038   $179.70   $179.70   $179.70  
  Purchase #4 $29.48   6.522%   $31.4027   $31.40   $31.40   $31.40  
  Purchase #5 $22.48   7.749%   $24.222   $24.22   $24.20   $24.20  
  Purchase #6 $209.62   5.759%   $221.692   $221.69   $221.70   $221.70  
  Purchase #7 $58.28   11.216%   $64.8167   $64.82   $64.80   $64.80  
  7 purchase totals = $851.32       $917.8019   $917.79   $917.75   $917.70