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 $158.27   12.310%   $177.753   $177.75   $177.75   $177.80  
  Purchase #2 $149.38   12.462%   $167.9957   $168.00   $168.00   $168.00  
  Purchase #3 $178.83   13.112%   $202.2782   $202.28   $202.30   $202.30  
  Purchase #4 $49.77   13.658%   $56.5676   $56.57   $56.55   $56.60  
  Purchase #5 $115.88   12.181%   $129.9953   $130.00   $130.00   $130.00  
  Purchase #6 $217.77   3.636%   $225.6881   $225.69   $225.70   $225.70  
  Purchase #7 $57.43   12.484%   $64.5996   $64.60   $64.60   $64.60  
  7 purchase totals = $927.33       $1,024.8775   $1,024.89   $1,024.90   $1,025.00