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 $137.86   10.116%   $151.8059   $151.81   $151.80   $151.80  
  Purchase #2 $103.60   9.346%   $113.2825   $113.28   $113.30   $113.30  
  Purchase #3 $76.28   6.311%   $81.094   $81.09   $81.10   $81.10  
  Purchase #4 $208.79   5.184%   $219.6137   $219.61   $219.60   $219.60  
  Purchase #5 $101.30   3.217%   $104.5588   $104.56   $104.55   $104.60  
  Purchase #6 $55.82   10.565%   $61.7174   $61.72   $61.70   $61.70  
  Purchase #7 $18.90   5.634%   $19.9648   $19.96   $19.95   $20.00  
  7 purchase totals = $702.55       $752.0371   $752.03   $752.00   $752.10