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 $61.25   13.601%   $69.5806   $69.58   $69.60   $69.60  
  Purchase #2 $23.33   9.420%   $25.5277   $25.53   $25.55   $25.50  
  Purchase #3 $151.52   10.120%   $166.8538   $166.85   $166.85   $166.90  
  Purchase #4 $71.79   4.372%   $74.9287   $74.93   $74.95   $74.90  
  Purchase #5 $229.44   10.397%   $253.2949   $253.29   $253.30   $253.30  
  Purchase #6 $120.82   9.116%   $131.834   $131.83   $131.85   $131.80  
  Purchase #7 $34.57   4.862%   $36.2508   $36.25   $36.25   $36.30  
  7 purchase totals = $692.72       $758.2705   $758.26   $758.35   $758.30