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 $58.31   8.459%   $63.2424   $63.24   $63.25   $63.20  
  Purchase #2 $96.48   13.292%   $109.3041   $109.30   $109.30   $109.30  
  Purchase #3 $49.71   3.759%   $51.5786   $51.58   $51.60   $51.60  
  Purchase #4 $201.57   3.599%   $208.8245   $208.82   $208.80   $208.80  
  Purchase #5 $219.32   10.854%   $243.125   $243.13   $243.15   $243.10  
  Purchase #6 $239.82   13.563%   $272.3468   $272.35   $272.35   $272.30  
  Purchase #7 $191.28   13.524%   $217.1487   $217.15   $217.15   $217.10  
  7 purchase totals = $1,056.49       $1,165.5701   $1,165.57   $1,165.60   $1,165.40