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 $64.52   12.459%   $72.5585   $72.56   $72.55   $72.60  
  Purchase #2 $187.67   4.244%   $195.6347   $195.63   $195.65   $195.60  
  Purchase #3 $187.47   11.372%   $208.7891   $208.79   $208.80   $208.80  
  Purchase #4 $6.66   8.777%   $7.2445   $7.24   $7.25   $7.20  
  Purchase #5 $43.94   7.615%   $47.286   $47.29   $47.30   $47.30  
  Purchase #6 $240.47   9.722%   $263.8485   $263.85   $263.85   $263.80  
  Purchase #7 $190.30   5.870%   $201.4706   $201.47   $201.45   $201.50  
  7 purchase totals = $921.03       $996.8319   $996.83   $996.85   $996.80