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 $152.86   10.360%   $168.6963   $168.70   $168.70   $168.70  
  Purchase #2 $217.52   8.292%   $235.5568   $235.56   $235.55   $235.60  
  Purchase #3 $151.57   3.488%   $156.8568   $156.86   $156.85   $156.90  
  Purchase #4 $18.31   7.563%   $19.6948   $19.69   $19.70   $19.70  
  Purchase #5 $197.56   5.463%   $208.3527   $208.35   $208.35   $208.40  
  Purchase #6 $66.27   12.299%   $74.4205   $74.42   $74.40   $74.40  
  Purchase #7 $236.28   7.764%   $254.6248   $254.62   $254.60   $254.60  
  7 purchase totals = $1,040.37       $1,118.2027   $1,118.20   $1,118.15   $1,118.30