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 $146.80   8.171%   $158.795   $158.80   $158.80   $158.80  
  Purchase #2 $133.99   13.501%   $152.08   $152.08   $152.10   $152.10  
  Purchase #3 $89.70   4.335%   $93.5885   $93.59   $93.60   $93.60  
  Purchase #4 $69.44   9.174%   $75.8104   $75.81   $75.80   $75.80  
  Purchase #5 $239.26   6.620%   $255.099   $255.10   $255.10   $255.10  
  Purchase #6 $60.46   5.292%   $63.6595   $63.66   $63.65   $63.70  
  Purchase #7 $216.34   8.474%   $234.6727   $234.67   $234.65   $234.70  
  7 purchase totals = $955.99       $1,033.7051   $1,033.71   $1,033.70   $1,033.80