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 $224.41   12.166%   $251.7117   $251.71   $251.70   $251.70  
  Purchase #2 $62.90   13.133%   $71.1607   $71.16   $71.15   $71.20  
  Purchase #3 $191.59   10.431%   $211.5748   $211.57   $211.55   $211.60  
  Purchase #4 $160.76   4.834%   $168.5311   $168.53   $168.55   $168.50  
  Purchase #5 $173.94   4.143%   $181.1463   $181.15   $181.15   $181.10  
  Purchase #6 $119.87   3.488%   $124.0511   $124.05   $124.05   $124.10  
  Purchase #7 $13.33   11.750%   $14.8963   $14.90   $14.90   $14.90  
  7 purchase totals = $946.80       $1,023.0720   $1,023.07   $1,023.05   $1,023.10