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 $60.27   4.424%   $62.9363   $62.94   $62.95   $62.90  
  Purchase #2 $196.41   11.464%   $218.9264   $218.93   $218.95   $218.90  
  Purchase #3 $246.72   13.395%   $279.7681   $279.77   $279.75   $279.80  
  Purchase #4 $74.52   6.209%   $79.1469   $79.15   $79.15   $79.10  
  Purchase #5 $117.39   8.641%   $127.5337   $127.53   $127.55   $127.50  
  Purchase #6 $24.55   7.232%   $26.3255   $26.33   $26.35   $26.30  
  Purchase #7 $51.39   11.582%   $57.342   $57.34   $57.35   $57.30  
  7 purchase totals = $771.25       $851.9789   $851.99   $852.05   $851.80