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 $43.73   13.638%   $49.6939   $49.69   $49.70   $49.70  
  Purchase #2 $192.66   12.162%   $216.0913   $216.09   $216.10   $216.10  
  Purchase #3 $51.56   10.231%   $56.8351   $56.84   $56.85   $56.80  
  Purchase #4 $59.61   3.781%   $61.8639   $61.86   $61.85   $61.90  
  Purchase #5 $121.74   10.576%   $134.6152   $134.62   $134.60   $134.60  
  Purchase #6 $148.66   12.654%   $167.4714   $167.47   $167.45   $167.50  
  Purchase #7 $40.84   9.768%   $44.8293   $44.83   $44.85   $44.80  
  7 purchase totals = $658.80       $731.4001   $731.40   $731.40   $731.40