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 $31.53   6.813%   $33.6781   $33.68   $33.70   $33.70  
  Purchase #2 $108.80   4.598%   $113.8026   $113.80   $113.80   $113.80  
  Purchase #3 $214.48   5.661%   $226.6217   $226.62   $226.60   $226.60  
  Purchase #4 $83.33   3.163%   $85.9657   $85.97   $85.95   $86.00  
  Purchase #5 $97.82   6.560%   $104.237   $104.24   $104.25   $104.20  
  Purchase #6 $247.27   4.298%   $257.8977   $257.90   $257.90   $257.90  
  Purchase #7 $24.79   11.609%   $27.6679   $27.67   $27.65   $27.70  
  7 purchase totals = $808.02       $849.8707   $849.88   $849.85   $849.90