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 $212.94   10.159%   $234.5726   $234.57   $234.55   $234.60  
  Purchase #2 $148.91   13.658%   $169.2481   $169.25   $169.25   $169.20  
  Purchase #3 $53.77   11.168%   $59.775   $59.78   $59.80   $59.80  
  Purchase #4 $85.91   7.584%   $92.4254   $92.43   $92.45   $92.40  
  Purchase #5 $58.45   5.562%   $61.701   $61.70   $61.70   $61.70  
  Purchase #6 $42.97   10.696%   $47.5661   $47.57   $47.55   $47.60  
  Purchase #7 $39.70   11.370%   $44.2139   $44.21   $44.20   $44.20  
  7 purchase totals = $642.65       $709.5021   $709.51   $709.50   $709.50