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 $235.36   12.360%   $264.4505   $264.45   $264.45   $264.50  
  Purchase #2 $126.32   4.229%   $131.6621   $131.66   $131.65   $131.70  
  Purchase #3 $34.42   10.103%   $37.8975   $37.90   $37.90   $37.90  
  Purchase #4 $58.80   3.437%   $60.821   $60.82   $60.80   $60.80  
  Purchase #5 $219.38   6.749%   $234.186   $234.19   $234.20   $234.20  
  Purchase #6 $175.34   13.385%   $198.8093   $198.81   $198.80   $198.80  
  Purchase #7 $74.32   7.469%   $79.871   $79.87   $79.85   $79.90  
  7 purchase totals = $923.94       $1,007.6974   $1,007.70   $1,007.65   $1,007.80