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 $168.47   11.565%   $187.9536   $187.95   $187.95   $188.00  
  Purchase #2 $142.26   7.544%   $152.9921   $152.99   $153.00   $153.00  
  Purchase #3 $90.70   5.823%   $95.9815   $95.98   $96.00   $96.00  
  Purchase #4 $41.90   10.840%   $46.442   $46.44   $46.45   $46.40  
  Purchase #5 $244.36   9.352%   $267.2125   $267.21   $267.20   $267.20  
  Purchase #6 $143.39   12.365%   $161.1202   $161.12   $161.10   $161.10  
  Purchase #7 $229.40   12.563%   $258.2195   $258.22   $258.20   $258.20  
  7 purchase totals = $1,060.48       $1,169.9214   $1,169.91   $1,169.90   $1,169.90