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 $92.44   10.593%   $102.2322   $102.23   $102.25   $102.20  
  Purchase #2 $48.45   11.361%   $53.9544   $53.95   $53.95   $54.00  
  Purchase #3 $49.43   11.488%   $55.1085   $55.11   $55.10   $55.10  
  Purchase #4 $195.38   4.264%   $203.711   $203.71   $203.70   $203.70  
  Purchase #5 $203.52   8.326%   $220.4651   $220.47   $220.45   $220.50  
  Purchase #6 $80.92   6.808%   $86.429   $86.43   $86.45   $86.40  
  Purchase #7 $50.29   6.658%   $53.6383   $53.64   $53.65   $53.60  
  7 purchase totals = $720.43       $775.5385   $775.54   $775.55   $775.50