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 $68.44   11.661%   $76.4208   $76.42   $76.40   $76.40  
  Purchase #2 $238.40   3.541%   $246.8417   $246.84   $246.85   $246.80  
  Purchase #3 $131.38   12.500%   $147.8025   $147.80   $147.80   $147.80  
  Purchase #4 $58.91   3.696%   $61.0873   $61.09   $61.10   $61.10  
  Purchase #5 $236.60   7.411%   $254.1344   $254.13   $254.15   $254.10  
  Purchase #6 $90.48   8.214%   $97.912   $97.91   $97.90   $97.90  
  Purchase #7 $65.55   6.864%   $70.0494   $70.05   $70.05   $70.00  
  7 purchase totals = $889.76       $954.2481   $954.24   $954.25   $954.10