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 $187.91   8.395%   $203.685   $203.69   $203.70   $203.70  
  Purchase #2 $85.96   6.535%   $91.5775   $91.58   $91.60   $91.60  
  Purchase #3 $92.33   5.671%   $97.566   $97.57   $97.55   $97.60  
  Purchase #4 $91.75   5.789%   $97.0614   $97.06   $97.05   $97.10  
  Purchase #5 $196.88   3.588%   $203.9441   $203.94   $203.95   $203.90  
  Purchase #6 $231.35   6.116%   $245.4994   $245.50   $245.50   $245.50  
  Purchase #7 $50.83   6.468%   $54.1177   $54.12   $54.10   $54.10  
  7 purchase totals = $937.01       $993.4511   $993.46   $993.45   $993.50