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 $54.82   8.488%   $59.4731   $59.47   $59.45   $59.50  
  Purchase #2 $99.33   6.312%   $105.5997   $105.60   $105.60   $105.60  
  Purchase #3 $240.68   11.204%   $267.6458   $267.65   $267.65   $267.60  
  Purchase #4 $193.94   8.761%   $210.9311   $210.93   $210.95   $210.90  
  Purchase #5 $211.81   5.787%   $224.0674   $224.07   $224.05   $224.10  
  Purchase #6 $68.68   3.113%   $70.818   $70.82   $70.80   $70.80  
  Purchase #7 $236.84   8.147%   $256.1354   $256.14   $256.15   $256.10  
  7 purchase totals = $1,106.10       $1,194.6705   $1,194.68   $1,194.65   $1,194.60