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 $92.36   13.315%   $104.6577   $104.66   $104.65   $104.70  
  Purchase #2 $6.91   12.546%   $7.7769   $7.78   $7.80   $7.80  
  Purchase #3 $80.73   5.566%   $85.2234   $85.22   $85.20   $85.20  
  Purchase #4 $87.85   6.160%   $93.2616   $93.26   $93.25   $93.30  
  Purchase #5 $45.71   6.469%   $48.667   $48.67   $48.65   $48.70  
  Purchase #6 $88.44   13.442%   $100.3281   $100.33   $100.35   $100.30  
  Purchase #7 $57.75   6.771%   $61.6603   $61.66   $61.65   $61.70  
  7 purchase totals = $459.75       $501.5750   $501.58   $501.55   $501.70