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 $169.61   9.373%   $185.5075   $185.51   $185.50   $185.50  
  Purchase #2 $245.68   7.397%   $263.8529   $263.85   $263.85   $263.90  
  Purchase #3 $80.40   13.237%   $91.0425   $91.04   $91.05   $91.00  
  Purchase #4 $179.58   12.835%   $202.6291   $202.63   $202.65   $202.60  
  Purchase #5 $178.83   3.757%   $185.5486   $185.55   $185.55   $185.50  
  Purchase #6 $23.39   8.856%   $25.4614   $25.46   $25.45   $25.50  
  Purchase #7 $77.29   5.337%   $81.415   $81.42   $81.40   $81.40  
  7 purchase totals = $954.78       $1,035.4570   $1,035.46   $1,035.45   $1,035.40