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 $36.74   3.694%   $38.0972   $38.10   $38.10   $38.10  
  Purchase #2 $79.49   9.786%   $87.2689   $87.27   $87.25   $87.30  
  Purchase #3 $18.60   8.188%   $20.123   $20.12   $20.10   $20.10  
  Purchase #4 $154.33   12.158%   $173.0934   $173.09   $173.10   $173.10  
  Purchase #5 $75.86   9.186%   $82.8285   $82.83   $82.85   $82.80  
  Purchase #6 $52.48   9.352%   $57.3879   $57.39   $57.40   $57.40  
  Purchase #7 $62.62   9.812%   $68.7643   $68.76   $68.75   $68.80  
  7 purchase totals = $480.12       $527.5632   $527.56   $527.55   $527.60