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 $61.63   11.369%   $68.6367   $68.64   $68.65   $68.60  
  Purchase #2 $201.91   8.683%   $219.4418   $219.44   $219.45   $219.40  
  Purchase #3 $86.76   11.753%   $96.9569   $96.96   $96.95   $97.00  
  Purchase #4 $214.79   9.118%   $234.3746   $234.37   $234.35   $234.40  
  Purchase #5 $51.69   9.114%   $56.401   $56.40   $56.40   $56.40  
  Purchase #6 $36.94   9.329%   $40.3861   $40.39   $40.40   $40.40  
  Purchase #7 $160.98   10.388%   $177.7026   $177.70   $177.70   $177.70  
  7 purchase totals = $814.70       $893.8997   $893.90   $893.90   $893.90