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 $70.62   6.135%   $74.9525   $74.95   $74.95   $75.00  
  Purchase #2 $236.65   9.543%   $259.2335   $259.23   $259.25   $259.20  
  Purchase #3 $51.26   7.270%   $54.9866   $54.99   $55.00   $55.00  
  Purchase #4 $98.27   3.260%   $101.4736   $101.47   $101.45   $101.50  
  Purchase #5 $233.68   11.112%   $259.6465   $259.65   $259.65   $259.60  
  Purchase #6 $116.52   10.518%   $128.7756   $128.78   $128.80   $128.80  
  Purchase #7 $24.26   8.602%   $26.3468   $26.35   $26.35   $26.30  
  7 purchase totals = $831.26       $905.4151   $905.42   $905.45   $905.40