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 $208.80   6.514%   $222.4012   $222.40   $222.40   $222.40  
  Purchase #2 $187.73   13.277%   $212.6549   $212.65   $212.65   $212.70  
  Purchase #3 $166.45   5.213%   $175.127   $175.13   $175.15   $175.10  
  Purchase #4 $87.92   4.279%   $91.6821   $91.68   $91.70   $91.70  
  Purchase #5 $73.68   3.449%   $76.2212   $76.22   $76.20   $76.20  
  Purchase #6 $174.51   10.868%   $193.4757   $193.48   $193.50   $193.50  
  Purchase #7 $38.26   7.584%   $41.1616   $41.16   $41.15   $41.20  
  7 purchase totals = $937.35       $1,012.7237   $1,012.72   $1,012.75   $1,012.80