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 $57.79   7.203%   $61.9526   $61.95   $61.95   $62.00  
  Purchase #2 $44.58   3.125%   $45.9731   $45.97   $45.95   $46.00  
  Purchase #3 $103.30   5.399%   $108.8772   $108.88   $108.90   $108.90  
  Purchase #4 $189.86   4.223%   $197.8778   $197.88   $197.90   $197.90  
  Purchase #5 $33.72   4.559%   $35.2573   $35.26   $35.25   $35.30  
  Purchase #6 $150.69   7.818%   $162.4709   $162.47   $162.45   $162.50  
  Purchase #7 $55.69   5.841%   $58.9429   $58.94   $58.95   $58.90  
  7 purchase totals = $635.63       $671.3518   $671.35   $671.35   $671.50