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 $60.39   4.522%   $63.1208   $63.12   $63.10   $63.10  
  Purchase #2 $235.90   13.161%   $266.9468   $266.95   $266.95   $266.90  
  Purchase #3 $57.50   4.874%   $60.3026   $60.30   $60.30   $60.30  
  Purchase #4 $208.39   9.652%   $228.5038   $228.50   $228.50   $228.50  
  Purchase #5 $100.29   5.310%   $105.6154   $105.62   $105.60   $105.60  
  Purchase #6 $157.35   13.107%   $177.9739   $177.97   $177.95   $178.00  
  Purchase #7 $141.88   4.499%   $148.2632   $148.26   $148.25   $148.30  
  7 purchase totals = $961.70       $1,050.7265   $1,050.72   $1,050.65   $1,050.70