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 $239.92   13.718%   $272.8322   $272.83   $272.85   $272.80  
  Purchase #2 $189.56   11.607%   $211.5622   $211.56   $211.55   $211.60  
  Purchase #3 $47.50   8.865%   $51.7109   $51.71   $51.70   $51.70  
  Purchase #4 $212.31   5.524%   $224.038   $224.04   $224.05   $224.00  
  Purchase #5 $8.48   4.574%   $8.8679   $8.87   $8.85   $8.90  
  Purchase #6 $168.56   3.803%   $174.9703   $174.97   $174.95   $175.00  
  Purchase #7 $55.31   3.233%   $57.0982   $57.10   $57.10   $57.10  
  7 purchase totals = $921.64       $1,001.0797   $1,001.08   $1,001.05   $1,001.10