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 $236.70   10.117%   $260.6469   $260.65   $260.65   $260.60  
  Purchase #2 $34.27   3.848%   $35.5887   $35.59   $35.60   $35.60  
  Purchase #3 $90.67   7.829%   $97.7686   $97.77   $97.75   $97.80  
  Purchase #4 $118.32   11.512%   $131.941   $131.94   $131.95   $131.90  
  Purchase #5 $108.79   10.464%   $120.1738   $120.17   $120.15   $120.20  
  Purchase #6 $228.60   10.415%   $252.4087   $252.41   $252.40   $252.40  
  Purchase #7 $147.89   4.868%   $155.0893   $155.09   $155.10   $155.10  
  7 purchase totals = $965.24       $1,053.6170   $1,053.62   $1,053.60   $1,053.60