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 $64.57   6.182%   $68.5617   $68.56   $68.55   $68.60  
  Purchase #2 $218.97   6.673%   $233.5819   $233.58   $233.60   $233.60  
  Purchase #3 $19.38   8.797%   $21.0849   $21.08   $21.10   $21.10  
  Purchase #4 $57.78   6.291%   $61.4149   $61.41   $61.40   $61.40  
  Purchase #5 $126.73   9.446%   $138.7009   $138.70   $138.70   $138.70  
  Purchase #6 $221.28   6.202%   $235.0038   $235.00   $235.00   $235.00  
  Purchase #7 $107.74   12.243%   $120.9306   $120.93   $120.95   $120.90  
  7 purchase totals = $816.45       $879.2787   $879.26   $879.30   $879.30