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 $85.27   10.828%   $94.503   $94.50   $94.50   $94.50  
  Purchase #2 $55.32   6.613%   $58.9783   $58.98   $59.00   $59.00  
  Purchase #3 $162.62   10.131%   $179.095   $179.10   $179.10   $179.10  
  Purchase #4 $214.94   3.823%   $223.1572   $223.16   $223.15   $223.20  
  Purchase #5 $47.28   12.387%   $53.1366   $53.14   $53.15   $53.10  
  Purchase #6 $96.67   9.829%   $106.1717   $106.17   $106.15   $106.20  
  Purchase #7 $249.69   5.823%   $264.2294   $264.23   $264.25   $264.20  
  7 purchase totals = $911.79       $979.2712   $979.28   $979.30   $979.30