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 $46.49   12.819%   $52.4496   $52.45   $52.45   $52.40  
  Purchase #2 $117.36   11.425%   $130.7684   $130.77   $130.75   $130.80  
  Purchase #3 $83.37   4.161%   $86.839   $86.84   $86.85   $86.80  
  Purchase #4 $177.39   8.857%   $193.1014   $193.10   $193.10   $193.10  
  Purchase #5 $48.28   13.201%   $54.6534   $54.65   $54.65   $54.70  
  Purchase #6 $205.82   9.326%   $225.0148   $225.01   $225.00   $225.00  
  Purchase #7 $23.81   3.689%   $24.6884   $24.69   $24.70   $24.70  
  7 purchase totals = $702.52       $767.5150   $767.51   $767.50   $767.50