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 $60.26   8.352%   $65.2929   $65.29   $65.30   $65.30  
  Purchase #2 $21.54   6.533%   $22.9472   $22.95   $22.95   $22.90  
  Purchase #3 $66.60   3.546%   $68.9616   $68.96   $68.95   $69.00  
  Purchase #4 $243.80   3.739%   $252.9157   $252.92   $252.90   $252.90  
  Purchase #5 $149.67   4.860%   $156.944   $156.94   $156.95   $156.90  
  Purchase #6 $234.68   5.436%   $247.4372   $247.44   $247.45   $247.40  
  Purchase #7 $44.39   5.462%   $46.8146   $46.81   $46.80   $46.80  
  7 purchase totals = $820.94       $861.3132   $861.31   $861.30   $861.20