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 $98.65   6.554%   $105.1155   $105.12   $105.10   $105.10  
  Purchase #2 $139.33   11.711%   $155.6469   $155.65   $155.65   $155.60  
  Purchase #3 $165.73   6.157%   $175.934   $175.93   $175.95   $175.90  
  Purchase #4 $247.76   8.392%   $268.552   $268.55   $268.55   $268.60  
  Purchase #5 $197.51   3.208%   $203.8461   $203.85   $203.85   $203.80  
  Purchase #6 $72.86   4.757%   $76.326   $76.33   $76.35   $76.30  
  Purchase #7 $164.57   11.363%   $183.2701   $183.27   $183.25   $183.30  
  7 purchase totals = $1,086.41       $1,168.6906   $1,168.70   $1,168.70   $1,168.60