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 $92.79   13.158%   $104.9993   $105.00   $105.00   $105.00  
  Purchase #2 $52.99   11.208%   $58.9291   $58.93   $58.95   $58.90  
  Purchase #3 $148.56   12.428%   $167.023   $167.02   $167.00   $167.00  
  Purchase #4 $26.57   9.318%   $29.0458   $29.05   $29.05   $29.00  
  Purchase #5 $135.62   12.502%   $152.5752   $152.58   $152.60   $152.60  
  Purchase #6 $145.44   7.109%   $155.7793   $155.78   $155.80   $155.80  
  Purchase #7 $143.81   5.393%   $151.5657   $151.57   $151.55   $151.60  
  7 purchase totals = $745.78       $819.9174   $819.93   $819.95   $819.90